The potential effects of climate change on southern calamary in
Tasmanian waters: biology, ecology and fisheries
Short paper produced for the World Wildlife Fund U.S.
Gretta T Pecl1 and George D Jackson2
1Tasmanian
Aquaculture and Fisheries Institute
University of Tasmania
Private Bag 49
Hobart, Australia 7001
2Institute
of Antarctic and Southern Ocean Studies
University of Tasmania
Private Bag 77
Hobart, Australia 7001
1
Corresponding author
Email:
Gretta.Pecl@utas.edu.au
Phone:
+61 3 62277277
Fax:
+61 3 62278035
1
Summary
Virtually every facet of squid life-history that has been examined thus far has revealed an
incredible capacity in this group for life-history plasticity. The extremely fast growth rates of
individuals and rapid rates of turnover at the population level mean that squid can respond
quickly to environmental or ecosystem change. Their ‘life-in-the-fast-lane’ life-style allows
them to rapidly exploit ‘vacuums’ created in the ecosystem when predators or competitors are
removed.
In this way they function as ‘weeds of the sea’ (Jackson and O’Dor 2001).
Elevated temperatures accelerate the life-histories of squid, increasing their growth rates and
shortening their life-spans. At first glance, it would be logical to suggest that rising water
temperatures associated with climate change (if food supply remains adequate) would be
beneficial to inshore squid fisheries – growth rates may increase, squid would be larger, and
turnover of populations more rapid. However, the response of inshore squid populations to
climate change is likely to be extremely complex. The size of hatchlings emerging from the
eggs becomes smaller as temperatures increase, and hatchling size may have a critical
influence on the size-at-age that may be achieved as adults, and subsequently population
structure. The influence of higher temperatures on the egg and adult stages may thus be
opposing forces on the life-history. The process of climate change will likely result in squids
that hatch out smaller and earlier, undergo faster growth over shorter life-spans, and mature
younger and at a smaller size. Individual squid will require more food per unit body size,
require more oxygen for faster metabolisms, and have a reduced capacity to cope without
food.
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Introduction
Cephalopod populations in our oceans appear to be expanding as world fisheries remove
their fish competitors and predators (Caddy and Rodhouse 1998). An appreciation of the role
of this group in the world’s marine ecosystems can be achieved by considering just how many
squid, octopus and cuttlefish there are in the ocean. The total biomass of this group has been
estimated to equal that of all species of fishes in the world’s oceans (Clarke 1987)! Many
different cephalopod species are targeted commercially, however, it is the migrating oceanic
ommastrephid squids and the inshore coastal loliginid squids that form the basis of major
cephalopod fisheries, and also play very important roles in the trophic structure of the worlds
marine ecosystems (Rodhouse and Nigmatullin 1996).
In many ways, squids are ecological equivalents to teleost fish. However, their physiology,
biochemistry, and life-histories are very different to their teleost competitors (O’Dor and
Webber 1986). Squids are geared to doing everything fast, with extremely fast growth rates,
short life-spans and therefore rapid turnover of populations. Squid life-spans are a fraction of
their teleost competitors - while some fish are now known to live for over a century, squids
generally rarely live longer than a year, and sometimes considerably less (Jackson in press).
Squids have some of the highest growth rates of poikilothermic animals,
several times
greater than that of fish and approaching homeothermic mammals (Lee 1994). To fuel such
incredible growth throughout their short lives (typically <1 year), their metabolic rates are
rapid (Seibel et al. 1997), and their appetites ravenous. Adult temperate species consume up
to 30% of their body weight per day in food, and juveniles up to a massive 72% (Segawa
1990). Unlike most fish, squids and other cephalopods have continuous growth throughout
their life-cycle without reaching an asymptotic size (Alford and Jackson 1993). At young ages
at least, growth is exponential where the growth trajectory concaves upwards and very small
differences between individuals in the early growth stages amplify throughout the life-span
(working like compound interest). As a group, cephalopods are becoming renowned for the
extreme flexibility and plasticity of their life-histories, largely a result of dramatic and direct
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responses of growth to temperature.
This flexibility is largely a function of the highly
responsive nature of squid physiology to environmental elements (Jackson and O’Dor 2001),
with temperature often cited as a key driving factor (Forsythe 1993). For example, Loligo
forbesi hatchlings reared at two temperatures with only 1oC difference resulted in squid that
were three times larger in the warmer group after 90 days than the cooler reared siblings
(Forsythe and Hanlon 1989).
With such profound and direct effects of temperature on the life-cycles and life-history of
squids, our emerging understanding of the crucial role of cephalopods in many ecosystems,
and the increasing commercial importance of this group, it is little wonder that many
researchers have begun to ponder the potential effects of climate change on squid
populations and fisheries. Forsythe et al. (2001) asked the obvious question of how squid
populations will react to ocean scale temperature change and urged future research in this
direction. Given that many species seem to tolerate and even thrive in warm conditions it has
been suggested that cephalopods, inshore loliginid squid in particular, will prosper with global
warming. Increased growth rates, accelerated life-histories, and rapid turnover in populations
could potentially lead to population expansion at the expense of slower growing teleost
competitors (Jackson in press). As short-lived species with plastic growth and reproduction,
and high mobility, they would better poised than many species or groups to respond to
changed balances in their environment (Boyle and Boletzky 1996). As a group, their potential
to adapt in one way or another will undoubtedly prove true, however, is our current perception
of the way squid populations may respond to climate change too simplistic?
By the end of the next century global mean sea surface temperatures (SST’s) are expected to
rise substantially (1-3.5oC, Watson et al. 1996 in Forsythe in press; 1.4 to 5.8 oC Schneider
2001). However, climate change may mean more than just temperature rises. Other
predictions with potential impacts on squid populations include an increase in extreme events
with more intense El Niño events possible, and more common El Niño like conditions
(Easterling et al. 2000). Rises in atmospheric CO2 are also expected, increasing surface
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ocean CO2 concentrations and resulting in an estimated drop in pH of about 0.4 units, which
may inhibit oxygen uptake of squids (Seibel and Fabry 2003). Abiotic changes in the world’s
oceans will result in concomitant changes in the biotic components as well. Global warming is
expected to increase thermal stratification of the upper ocean thereby reducing the upwelling
of nutrients and decreasing productivity (Seibel and Fabry 2003). Indeed, the warming of
some oceans has already been accompanied by a 70% decline in zooplankton abundance
(Roemmich and McGowan 1995). There appears to be a non-linearity in the response
between physical and biological processes, in that a small change in temperature can be
amplified into profound change in the abundance of zooplankton, micronekton and its
predators (Veit et al. 1997). Changes in temperature will also have indirect effects in addition
to direct impacts on the metabolism of species, affecting the abundance and activity rates of
predators (Bailey and Houde 1989).
The cumulative effects of climate change on marine ecosystems are already evident with
populations showing changes in the timing of life-cycle events (Beaugrand and Reid 2003)
and shifts towards higher latitudes according to thermal preferences (Daufresne et al. 2003).
There has also been widespread documented biological changes in the 20th century including
changes in species abundance, distribution, morphology, behaviour and community structure
(Easterling et al. 2000). Changes in the distribution of cephalopods has already been noted,
with the sudden appearance of subtropical and tropical species in temperate Galician waters
– including the squid Alloteuthis Africana and the common paper nautilus Argonauta argo, an
effect attributed to increase in SST of north-eastern Atlantic (Guerra et al. 2002).
The purpose of this discussion paper is to explore how climate change may impact on the lifehistory characteristics and population dynamics of inshore squid, and ultimately impact on our
inshore squid fisheries. Recently there has been much research into the life-history and
fisheries biology of the southern calamary, Sepioteuthis australis. This is now one of the
better understood inshore squid species in the world, and we therefore use this species as a
case study.
5
(I) Southern calamary and the fishery in Tasmania
Southern calamary are a shallow water species, endemic to southern Australian and northern
New Zealand waters. It is one of the most common cephalopods in the coastal waters of
southern Australia, and is commercially harvested in Tasmania, South Australia, Victoria and
New South Wales. In Tasmania, southern calamary are targeted as part of the multi-species
Tasmanian Commercial Scalefish Fishery (TCSF) and are taken commercially along the north
and east coasts of Tasmania and off Flinders Island, with the greatest proportion of the catch
taken in the central east coast region (Great Oyster Bay and Mercury Passage) (Figure 1).
The TCSF consists of a wide range of operator types, with calamary fishers falling under the
category of what has been described as high market price ‘artisanal’ or ‘cottage’ type
owner/operators using aluminium boats under 6 meters in length (Bradshaw 2003). In total,
the TSCF engages around 150 full time fishers comprising approximately 400 people. The
total catch for the 35 species targeted in the TSCF was 1,319.4 tons in 2001/02 (down from
over 2,000 tons in the early 1990’s), with southern calamary the third highest component of
around 103 tons (up from under 10 tons in the early 1990’s), or about 8% of the fishery (Lyle
2003).
Rising prices (from $4.50-$12 AUD) and expanding markets have led to dramatic increases in
both catch and effort for southern calamary. Catch and effort have tripled in the last 5 years
and there are concerns about sustaining such high levels of exploitation (Lyle, 2003, Figure
2). Management concerns have led to the introduction of short-term closures of the major
spawning areas, ranging from rolling two-week closures to a three-month block closure. The
southern calamary fishery in Tasmania is very small by international standards, most other
inshore squid fisheries around the world are in the order of around 2,200-15,000 tons
(Roberts et al. 1998). However, to the small population of Tasmania, and in particular the
smaller coastal fishing towns on the east coast, it is considered very important (Bradshaw
2003).
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Southern calamary are fished during the day over shallow areas of seagrass and macro algae
(<10m depth) using a variety of methods including purse seine, beach seine, spear, and dip
net, however, squid jigs on hand lines are the primary method (Lyle 2003). For the main part,
the fishery targets spawning aggregations, and most of the spawning activity on the east
coast of Tasmania is concentrated in Great Oyster Bay (Moltschaniwskyj and Pecl 2003),
which is an area of convergence between warm, nutrient poor East Australian Current (EAC)
water of sub-tropical origin and cool, nutrient rich water of sub-Antarctic origin (Harris et al.
1987).
Southern calamary are a fast growing, short-lived (<1 year) and multiple spawning inshore
species although, as with all other loliginid squids, we have no information about the
frequency of egg deposition or how many batches may be laid (Pecl 2001). Low levels of
spawning take place throughout the year, however, there is a distinct observable peak in the
austral spring and summer (Oct-Jan) when southern calamary aggregate over shallow
inshore spawning grounds (Moltschaniwskyj and Pecl 2003). All life-history characteristics of
southern calamary examined to date are highly variable, including, egg size and embryo
mortality (Steer et al. 2002), annual egg production of populations (Moltschaniwskyj and Pecl
2003), hatchling size (Steer et al. 2003a), level of reproductive investment (Pecl 2001), and
growth (Pecl in press).
(II) Climate change and southern calamary
The abiotic and biotic effects of ocean-scale climate change will have functional implications
at the species, population, and ecosystem level. In this paper we take a ‘bottom-up’
approach, firstly examining how climate change may impact on the physiology of individuals,
thereby altering their life-histories. We then discuss how these individual-level effects may be
consequently expressed at the population-level.
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(1) Individual effects
To examine potential effects of climate change at the individual level, we consider squid at
several developmental stages as it is likely that environmental variables, temperature for
example, will influence each life-history stage quite differently. We therefore deal with the
following discrete developmental stages separately, A) embryonic development and hatching,
B) post-hatching growth, and C) spawning adults.
(A) The embryonic and hatching phases
Mature southern calamary spawn large, individually encapsulated eggs, collective packaged
in gelatinous material and forming strands of 3 to 9 eggs (Steer et al. 2003b). Strands are
attached directly to seagrass, macro algae holdfasts, or embedded directly into the sand.
Most commonly eggs are attached to Amphibolis seagrass, with many strands laid together to
form egg mops of several to hundreds of strands (Moltschaniwskyj et al. 2003). The short
life-span of squid means that the success of the next generation relies entirely on the capacity
of each generation to produce viable offspring (Boyle and Boletzky 1996). For this reason
alone, factors affecting the embryonic and juvenile phases will have crucial impacts on
population success. Additionally, the embryonic phase of southern calamary is around 1-2
months (Steer et al. 2003b), and thus represents a significant portion of the entire life-span
(10-12 months, Pecl in press).
As temperatures increase, development times of cephalopod eggs decrease (Boletzky 1994),
provided that temperatures do not fall outside thermal tolerance boundaries (Gowland et al.
2002). However, although hatchlings emerge quicker under elevated temperatures, there is a
negative relationship between incubation temperature and hatchling size (Vidal et al. 2002),
so that the under warmer temperatures hatchlings emerge smaller (eg: Sepioteuthis australis,
Steer et al. 2003a). Within a single spawning season, southern calamary hatchlings emerging
at the start of the season (cooler) may be as large as 0.057g, whilst at the end of the
spawning season (warmer) hatchlings may be as small as 0.023g – only 40% of the size of
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the cooler hatchlings (Pecl et al. in press a). Warming oceans may therefore see a
downwards shift in the size of squid hatchlings emerging from inshore spawning grounds.
(B) Post-hatching growth
Smaller southern calamary hatchlings may mean smaller adults, or at least no net increase in
size-at-age, even if growth rate is substantially elevated by temperature. The effect of
temperature on the growth rate of individuals, providing food is not limited, is very clear warmer temperatures will promote faster growth over shorter life-spans (see Forsythe in
press). However, as growth in juvenile cephalopods is exponential, growth works like
compound interest on an investment, and the starting size of the investment is crucial. For
example, a 0.023g hatchling growing at 10% body weight per day would be 186g after three
months, whereas a 0.057g hatchling growing at the same rate would be 462g after the same
time period. If elevated temperatures reduced hatchling size to say, 0.01g, a hatchling of this
size growing at 10% would only be 81g after three months! To maintain adult size-at-age
under elevated temperatures, the 0.01g hatchling would have to grow at 11% to catch up to
the 0.023g hatchling.
Thus, the effects of elevated temperatures on the hatchling size and
post-hatching growth rate will likely be opposing forces on the size at age of adult squid (see
Figure 3).
Temperature driven changes in metabolic rate are directly coupled with feeding rate and
growth rate (Forsythe 1993). Growth rate however, may increase or decrease depending on
the nature of the food x metabolism x temperature relationship (Brett 1979). Not all species
will grow faster under increased temperatures, as increased temperatures may decrease
growth rate through either insufficient food supply, or reduced growth potential (see Jackson
and Moltschaniwskyj 2001a). Some species that grow slower in warmer waters may be at
their physiological limits with respect to temperature resulting in reduced growth rates (eg:
Loliolus noctiluca Jackson and Moltschaniwskyj 2001b). With respect to growth of southern
calamary, we know that:

Summer hatched grow faster than those hatched in winter (Pecl in press).
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
Warmer years may give rise to faster growing squid, although slow growers may still be
present. Growth rate variance also appears greater in warm years (Pecl et al. in press b).

Life-history plasticity is sex-specific. Males vary more in size and growth, while females
vary more in condition and level of reproductive investment (Pecl et al. in press b).

Southern calamary in warmer lower latitude populations (NSW, Australia) grow
faster (Pecl 2000). Genetic differences between locations may also influence
growth in Southern calamary (Triantafillos and Adams 2001, Triantafillos in press).
Thus, with respect to potential changes in growth rate of the Tasmanian population under a
regime of elevated temperatures, several outcomes (not mutually exclusive) are possible.
Firstly, if individuals are able to obtain sufficient resources (both food and oxygen, see below)
growth rates will increase (more so for males) as will variance in growth rate. However, adult
size may not necessarily increase as hatchling size, the starting point, will decrease. Under
continued temperature elevation, there will likely come a point where growth rates start to
decrease as metabolic costs continue to escalate and growth potential is subsequently
reduced. Secondly, as a function of increased growth rate, it is very likely that the average
life-span of squid will decrease (eg: Loliolus noctiluca Jackson and Moltschaniwskyj 2001b)
and individuals will mature younger and at a smaller size (eg: Sepioteuthis lessoniana,
Jackson and Moltschaniwskyj 2002).
Metabolic considerations – Owing to the high metabolic rates of squids, growth costs are
likely to dominate energy flux through an individual cephalopod (Wells and Clarke 1996). In
general, squid eat more and grow more rapidly than fish at comparable sizes and
temperatures (Forsythe and Van Heukelem 1987). Gross growth efficiency is also
exceptionally high for poikilotherms, estimated at between 20-30% for squid (O’Dor and Wells
1987). Feeding rates increase with temperature, however there is no empirical evidence that
food conversion rates change detectably with temperature (Wells and Clarke 1996). Adult
squid eat a large percentage of their body weight in food per day eg; Loligo opalescens 1518% (Yang et al. 1986) and the much larger Dosidicus gigas 13.1% (Erhardt 1991).
Hatchlings are even more voracious with Sepioteuthis lessoniana hatchlings for example
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consuming up to 72% of body weight in food per day (Segawa 1990). Failure to feed for even
short periods is disastrous for animals with such high metabolic rates and low levels of
metabolic reserves (Rodhouse and Nigmatullin 1996). The time period that new hatchlings
can survive without food is also shorter at higher temperatures (eg: Dosidicus gigas, Ichii et
al. 2002). Under a regime of elevated temperatures, smaller hatchlings would therefore need
more food but have less time in which to find it before facing mortality. In this way,
productivity changes may shift the temperatures defining thermal limits for species (Welch et
al. 1998).
Responses to prey and productivity – Potential changes to the productivity of the world’s
oceans are also of concern with respect to squid populations. This can be illustrated with the
Loligo opalescens population off California. Jackson and Domeier (2003) demonstrated that
although temperatures were much higher during the El Niño event, squid had slower growth
rates and were strikingly smaller from lack of food due to drastically reduced productivity
associated with a cessation of upwelling.
When the environment changed to La Niña
conditions with resumption of upwelling, increased productivity and abundant food, squid
grew faster and much bigger due to the increased prey, despite cooler temperatures.
Additionally, Piatkowski et al. (2002) reported that the biomass of cephalopods ingested by
seals in Antarctica decreased during El Niño years, although this may have been caused by
other factors and may not necessarily reflect reduced prey availability for the cephalopod
populations.
Squid are trophic opportunists that can occupy broad trophic niches and exploit the temporal
and spatial variability in prey populations. So although squid need vast quantities of prey, they
have a greater trophic flexibility than most other groups and this may help them to still prosper
during periods of reduced productivity. Squid can feed equally effectively on small
macrozooplankton or on fish that may be larger than themselves (Rodhouse and Nigmatullin
1996). Many cephalopods are cannibalistic and southern calamary is no exception (Jackson
and Pecl 2003). Indeed, from an individual perspective cannibalism may not be a bad option
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– Segawa (1990) found that growth of Sepioteuthis lessoniana hatchlings was greatest when
fed conspecific hatchlings (compared with fish and mysids).
Physiological considerations – Experimental data has shown that oxygen consumption of
squid increases linearly with body weight, while metabolism increases continuously in
association with increases in temperature (Segawa 1995). This means that energetically,
smaller squid do better at higher temperatures and large squid do better at lower
temperatures (O’Dor and Wells, 1987). Many species show intra-school cannibalism, which
may be an alternative to reducing metabolic rate when food is unavailable (O’Dor and Wells
1987). However, under a scenario of climate change, even if squid can obtain sufficient food
(by either being such flexible trophic opportunists, or by eating each other) to maintain
increased metabolism, will they be able to obtain sufficient oxygen to fuel metabolic
requirements? Respiratory proteins are very sensitive to changes in pH, with large decreases
in oxygen affinity as pH decreases. Climate change may result in a reduction in seawater pH
due to elevated CO2 and this will result in a decreased ability to bind oxygen for transport to
the tissues (Seibel and Fabry 2003). Such expected changes in ocean pH are sufficient to
impair oxygen transport and limit scope for activity in energy-hungry squids (Seibel and Fabry
2003). This could impact individual squid via disturbances to acid-base balance, oxygen
transport and metabolic processes, with cascading effects of growth, reproduction and
survival (Seibel and Fabry 2003).
(C) Adult spawning phase
It is not clear how elevated temperatures or changes in productivity may alter the reproductive
output of southern calamary, and how this in turn may impact on the population dynamics of
subsequent generations. Methods for estimating fecundity are poorly developed for
cephalopods (Boyle 1990), as is an assessment of how they distribute reproductive effort
through time and space (Pecl 2001). However, we know that large-bodied Sepioteuthis that
grow through cool conditions will have larger gonads and greater reproductive output
compared to their warm wanter counterparts. Warm-water squids will have a greater relative
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gonad investment with a higher percentage of their body weight as reproductive tissue, even
though in absolute terms their gonads will weigh less (Jackson and Moltschaniwskyj 2002,
Pecl 2000). However, we don’t know if this potential drop in fecundity will be overridden by
increased number of spawning episodes fuelled by a more rapid production of gametes. We
currently have no information about how the batch frequency or total number of eggs
deposited may be affected by temperature, food availability or life-span. It is likely that food
availability may be a more crucial determinant of reproductive allocation (Ho et al. in press,
Pecl et al. in press b). Based on what we know from past work, global warming will produce
squid that grow faster but have a smaller body size (due to reduced hatchling size and a
reduction in the time taken to reach maturity) and mature younger (Figure 4). This in turn will
increase physical constraints on just how much gonad a squid can produce. While the warmwater squid will have greater relative gonad investment, each individual will be smaller so
absolute gonad output may be less. Furthermore, different sized adult squids could also
change the social and behavioural aspects of courtship, mating and egg-laying.
(2) Population effects
Because of the numerous and obviously complex interactions, predicting the potential
outcomes of environmental change on discrete populations or species is not straightforward
(Clark et al. 2003). No species lives in an ecological vacuum, and although the link between
physiology and thermal tolerance can set theoretical distribution limits, the boundaries to
geographical ranges are typically set by other factors – including competitive interactions,
suboptimal physiological performance (Clarke 2003), and in some circumstances, habitat
availability. In the context of the current paper, we are interested in A) potential changes to
the absolute biomass of the southern calamary population, B) shifts the timing of peak
abundance, C) shifts in the location of peak abundance or alterations to overall distribution or
range, and D) the impact of any of these changes on the rest of the ecosystem of which
southern calamary are a part.
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A) Biomass
Squid fisheries are well known for their highly variable recruitment and catches, which creates
uncertainty for resource managers and the fishing industry, due to increased risk of stock
collapse. Large fluctuations in catch of the inshore squid Loligo bleekeri (eg: 40 fold,
Natsukari and Tashiro, 1991) are apparently unrelated to fishing effort (Beddington et al.
1990). The population dynamics of cephalopods are principally influenced by phenotypic
plasticity in response to environmental variation (Boyle and Boletzky 1996), although the
mechanisms and links through which this occurs are not well understood (Pecl et al. in press
b). Biomass changes quickly throughout a year and between years, and it is very likely that
climate change will have significant impacts on absolute biomass. Although several studies
have sought to establish relationships between environmental variables and cephalopod
biomass, this has not been overly successful and predictions of cephalopod abundance on an
annual basis are not yet possible. This makes sensible suggestions of how biomass may
change under a scenario of climate change quite difficult. The absolute level of biomass may
be affected by the carrying capacity of the evolving ecosystem. If productivity is decreased for
example, the rate of cannibalism within southern calamary populations will likely increase so
that fewer individuals will do well, however, biomass may be reduced if the level of
cannibalism is high.
B) Timing of peak abundance
Global warming may alter both timing and location of peak abundance. Timing of peak squid
abundance advances by 120-150 days in warmest years compared to coldest for Loligo
forbesi in the English Channel (Sims et al. 2001). Cephalopod biomass production is strongly
cyclical and usually an annual phenomenon except in some small and or tropical species
(Boyle and Boletzky 1996). Climate change will likely result in life-spans that are shorter, and
there is the possibility that temporal synchronicity of spawning activities of the population may
be reduced. Currently, southern calamary have a 10-12 month life-span (including embryonic
stage) and as a function of low levels of spawning all year, and batch spawning of females
throughout the main spawning season, squid enter the spawning grounds throughout the
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spring-summer spawning season in waves of ‘micro-cohorts’ (Figure 5a, Jackson and Pecl
2003). If life-spans are reduced, spawning activities may become less synchronised and the
production of biomass may become more complicated (Figure 5b). Shorter life-spans and
higher temperatures may even result in almost continuous aseasonal breeding and therefore
recruitment as currently occurs in tropical environments (Figure 5c). The synchronisation of
breeding activities may however, also be related to other environmental cues such as day
length. The manner in which synchronisation of spawning activities, and subsequent effects
on biomass, actually alter under a scenario of elevated temperatures (like a sub-tropical or
tropical environment) but continued seasonal cues (like day length in temperate
environments) remains obviously unknown.
Many temperate loliginids lay eggs so that the hatchlings emerge at the peak of production,
and while temperatures increase so that hatchlings may grow fast whilst feasting on an
abundance of prey (eg: Loligo vulgaris reynauldii, Sauer et al. 1992). Any de-synchronisation
of peak spawning and peak productivity may have implications for juvenile growth rate and
survival. Spring blooms can be characterised by peak amplitude, timing of peak, timing of
initiation and duration (Platt et al. 2003) – how these factors alter in Tasmania with climate
change may impact substantially on the success of each years spawning.
C) Location of peak abundance and range shifts
Climate change may influence population movements by altering temperature, quality and
quantity of food, or in the case of benthic spawning squids, altering the characteristics of the
seafloor habitat. The life-style of loliginid squids is intimately linked with the seabed, as they
lay compact egg masses attached to the bottom (Boyle 1990). Southern calamary spawning
activity is closely associated with Amphibolis seagrass, and any alterations in distribution of
spawning aggregations as a function of climate change may be tightly linked to changes in
Amphibolis distribution.
Species may also avoid warmer waters simply because food
supplies are insufficient to maintain such high metabolic rates, as has been suggested for
salmon (Welch et al. 1998). Researchers suspect that, as with most other loliginids, deep-
15
water spawning also occurs in southern calamary. As temperatures increase, if southern
calamary have distinct thermal preferences they may move further south, to cooler waters, or
they may move to deeper waters. We do not have any information about the extent to which
any inshore-offshore migrations may take place in southern calamary.
There are two genetic types of calamary, and a hybrid, that have been detected within the
Australian distribution (Triantafillos and Adams 2001). Southern calamary in NSW are a
different genetic type (‘peripherals’) to Tasmania (‘centrals’) (Triantafillos and Adams 2001).
With elevated temperatures, or changes in prey distribution and abundance, the ranges of the
two types of southern calamary may shift. The genetic type of southern calamary found at
higher latitudes may move south to lower latitudes. This could result in a very complex
population structure and may impact on the reproductive potential of the population if the two
genetic types overlapped, as the hybrids are thought to be reproductively sterile.
D) Ecosystem effects
Squid have high production to biomass ratios (O’Dor 1992), and one constraint on their lifecycle is the heavy pressure placed on the ecosystem through predation by large squid
populations (Roberts et al. 1998). Predation by a strong cohort of cephalopods on early
stages of commercial fish is likely to be a variable affecting the recruitment success of fish
stocks (Rodhouse and Nigmatullin 1996). Plainly, large schools of squid can have a very
significant impact on fish and crustacean populations. Energy used by a population equals
the population density multiplied by metabolic requirements of each individual (Knouft 2002).
Individual squid will be eating more per unit size as temperatures increase, so any stock of a
given size may place greater demands on the rest of the ecosystem at a higher temperature
than at a lower temperature.
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(3) Impacts on the fishery in Tasmania
When considering the issue of climate change and potential effects of this global
phenomenon on the life-history, population biology, and fisheries of inshore squid, it needs to
be highlighted that different degrees of certainty come into play when discussing various
pieces of this complex puzzle. For example, the impacts of elevated temperature on the
embryonic duration, size of hatchlings, and growth of adults, are well known and have a solid
physiological basis. Thus, many of the ways in which individual components of climate
change in isolation may impact on the lives of individual squid can be estimated with a
reasonable degree of certainty. However, while population and individual-level processes are
intimately linked, we unfortunately have a poor understanding of factors structuring and
regulating cephalopod populations. The complexity of ecological interactions renders it very
difficult to extrapolate from studies of individuals or populations to the community or
ecosystem level (Walther et al. 2002). As cephalopods are ‘ecological opportunists’, it is
even more difficult to suggest with any certainty what the impacts of climate change will be on
aspects of their population or fishery biology.
Notwithstanding the above, this discussion paper raises several issues concerning the
potential impacts of climate change on southern calamary life-history and populations, which
may have relevance for resource managers and fishers that depend on the resource:
 If generation times are shorter will southern calamary still exhibit aggregative spawning
behaviour? Will spawning aggregations become less spatially and temporally predictable? If
synchronicity of spawning activities is reduced, are miss-matches between peaks in spawning
activity and peaks in production likely? Changes in the characteristics of spawning
aggregations will have impacts on subsequent population dynamics, and also to the fishery
itself. Spawning aggregations are very easy and cost effective for fishers to target, if
aggregations are less predictable, or less dense will fishers shift to other already
overexploited resources?
 Will the location of peak abundance shift? This could occur either 1/ further south towards
the major population centre of Hobart, and away from coastal fishing towns on east coast, or
17
2/ into deeper and therefore cooler water further away from the coast, and less accessible to
small-scale fishers in 6m boats.
 Will the peak in spawning become harder to predict? Currently the main management
objective is to provide protection to spawning adults via short-term closures to ensure each
generation deposits sufficient eggs. Any changes in the predictability of spawning activities
will necessitate changes to management strategies.
 Climate change will have substantial impact on the size of individuals, this needs to be
monitored and considered in management evaluations as body size will alter correct
interpretation of both effort and catch per unit effort (CPUE) assessments of the fishery (Pecl
et al. in press b). The effort and CPUE statistics for a population made up of 300g individuals
will be very different to that of a population made up of 3000g individuals.
 If the ‘peripheral’ and ‘central’ genetic types (Triantafillos and Adams 2001) have different
thermal preferences, and the distribution of the two types alters in accordance with these
thermal preferences, Tasmania could see a different genetic type, or mix of genetic types
present. This would considerably complicate management of the resource. The ‘peripheral’
type of southern calamary may have a reproductive strategy more towards the terminal end of
the spawning continuum (Pecl 2001), and may therefore require a different management
strategy to the other multiple spawning type of calamary currently found in Tasmanian waters.
Additionally, hybrids of the two types appear to be reproductively compromised (Triantafillos
and Adams 2001), and so substantial mixing of the two types may lower the reproductive
output of the population.
The southern calamary inshore jig fishery is an integral part of the Tasmanian Commercial
Scalefish Fishery. There are several hundred licences for this whole fishery, and although of
relatively low total value compared to abalone or rock lobster, it is of crucial importance for
regional employment in Tasmania. The total annual value of the calamary component of the
fishery at first point of sale is approximately $1,000,000. Fishers receive $7 -12kg, making
calamary one of the highest value species in the Tasmanian Scalefish Fishery. Individual
owner/operators gross an average of $55,000 AUD (across all species caught within the
18
fishery), and boat hands are paid a percentage of the catch from 14-30% (Bradshaw 2003).
Many fishers fish exclusively near their home base, and distribution of home bases is skewed
towards regional areas – many said most of their expenditure associated with fishing occurs
within their home region (Bradshaw 2003). Southern calamary is also a key recreational
species in Tasmania, with recreational fishers taking approximately one-third the catch of
commercial fishers (Lyle and Haddon 2003).
Ecologically, the importance of southern calamary should not be under-estimated. It is a
major component in the diet of pilot whales and bottlenose dolphins (Gales and Pemberton
1992). Unspecified squid are also major prey items in Australian fur seals, Minke whale,
southern right whale dolphin, killer whale and porpoise in Tasmania or southeast Australian
continental shelf (Davenport and Bax 2002). All major predator groups (sharks, fishes and
marine mammals) rely on squid populations as a significant component of their diet (Smale
1996).
Conclusions?
The potential impacts of climate change at the individual, population and fishery level
discussed here for southern calamary in Tasmania have a much broader relevance than this
specific species at this location. Inshore squid species with similar life–history characteristics,
also targeted as part of multi-species artisanal fisheries, occur throughout the world on the
northeast seaboard of North America, the Pacific coast of South America, the south coast of
Africa, and small seaports along the European Atlantic and Mediterranean oceans. In
temperate waters the next 100 years will see over 100 generations of these highly responsive
creatures, in comparison to a handful of generations for sharks, tuna, or other larger
predators of our oceans. Squids, and cephalopods in general, have the intrinsic flexibility to
adapt to climate change - their life-history and physiological traits enable them to be
opportunists in variable environments (Rodhouse and Nigmatullin 1996). Additionally, we will
not have to wait decades to determine what these effects are. For species where we have
established good baseline data, changes will be immediately obvious, generation by
19
generation. In longer-lived predators it will however, take decades to establish cause and
effect on their life-histories, populations and abundance. Whilst definite answers to our
questions about ocean-scale climate change and the potential impacts on inshore squid
population dynamics or fisheries biology are impossible, one thing is for certain, and that is
that the pace of life for this high-speed group will increase even further.
Acknowledgements
We would like to thank Alan Jordan and Jeremy Lyle for constructive comments on this
report. Thankyou also to Sean Tracey for producing the figures, and Jason Bedelph for
technical assistance.
20
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25
AUSTRALIA
40°S
LAUNCESTON
TASMANIA
Catch
(Tonnes / year)
Great
Oyster
Bay
42°S
Mercury
Passage
20 – 50
5 – 20
1–5
0–1
< 5 fishers
HOBART
146°E
148°E
Figure 1: Total catch of southern calamary per fishing grid, for the 12 month period 2002/03.
Values based on monthly General Fishing Returns. Data cannot be shown where less than 5
boats reported catches.
26
1600
120
Catch (tonnes)
catch
effort
1200
80
1000
800
60
600
40
400
20
200
0
0
80/81
83/84
86/87
89/90
92/93
95/96
98/99
01/02
Figure 2: Annual catch (tonnes) and effort (fisher days) for the calamary component of the
Tasmanian Commercial Scalefish Fishery since 1980/81.
27
Effort (fisher days)
1400
100
Figure 3: The impact of initial hatchling size on the size-at-age that can be achieved at
different percentage daily growth rates. The effect of initial hatchling size becomes more
obvious as growth rates increase. Growth rates would likely increase with elevated
temperatures.
28
A
B
Figure 4: Schematic diagram showing potential effects of elevated temperatures on the lifehistory of southern calamary. A) Warmer temperatures are expected to reduce embryonic
duration, reduce hatchling size, increase growth rates, and shorten the overall life-span.
Maturation is at smaller sizes and younger ages. B) Cooler temperatures result in a longer
embryonic duration, larger hatchlings, and slower growth over a longer life-span, leading to a
larger final size. Maturation is at larger sizes and older ages.
29
Figure 5: Diagrammatic representation of fluctuations in biomass of squid over a one year
period. A) Aggregative spawning over an extended spawning season of up to several months
resulting in successive waves of recruitment, however, a clear peak is present, B) Breeding
season is extended beyond a few months as the life-span of squid becomes shorter, although
seasonal peaks in biomass production are still evident, C) Uncoupling of seasonal and
synchronous spawning cues resulting in aseasonal continuous recruitment with no obvious
peaks in biomass production (as occurs in tropical environments). This diagram is largely
adapted from that of Boyle and Boletzky 1996.
30