Chisholm
Associates
PO Box 11-014, Dunedin.
Ph/Fax: 03 454-4442
Mobile 027 221-4739
e-mail: bill@chisholm.co.nz
Editor - New Zealand Freshwater Sciences Society Newsletter
Hannah Rainforth
204 Anzac Parade
Whanganui 4500
h.rainforth@gmail.com
14th September 2009
Dear Hannah
As consultant to the South Island Eel Industry Association, and a member of NZFSS,
I am compelled to respond to the articles in the August NZFSS newsletter relating to
banning commercial eel fishing. I have just completed the “South Island Eel Industry
Association - Eel Fishery Plan for the South Island” which contains the policies and
actions that the South Island commercial eel fishermen will undertake, to maintain
and enhance a sustainable eel fishery. Copies of this Plan and all other reports
referenced in this letter are available through emailing me at bill@chisholm.co.nz.
For those who care to read this Plan, it will become immediately noticeable that
commercial eel fishermen have more at stake in maintaining sustainable eel fisheries
(shortfin and longfin) than anyone else in the country. The purpose of the Eel Fishery
Plan is to clearly outline the measures which commercial fishermen will undertake to
ensure the sustainability of their eel fishery. This includes doing considerably more
than merely labelling longfin eels as “threatened”, something which the South Island
Eel Industry Association strongly objects to on the grounds that it is arbitrary,
unscientific and essentially futile.
It would appear that Drs Joy and McEwen have based their conclusions and
recommendations (to ban commercial eeling) on the results of electrofishing surveys
of some lower North Island waterways (e.g. the Hutt River), and extracts from various
reports. Electric fishing is known to be less than 100% effective in catching eels (e.g.
Chisnall 1992), and overseas research frequently reports that eels are the most
difficult fish species to catch using electric fishing (e.g. Beaumont et al 2002). Glass
eels and elvers can be damaged by electric fishing. Repeat surveys may find fewer
juvenile eels because they will avoid further damage by burrowing deeper into the
substrate. Consequently, I have serious doubts that repeated electric fishing surveys
can provide measures of juvenile eel populations with any degree of accuracy.
I agree that elver recruitment monitoring at hydro dams has not been accurate, despite
indications that eel recruitment trends have been stable or increasing at most sites for
the last 8 years. Sampling methods have changed over this time (i.e. become more
efficient at catching elvers), and longfin eels are known to have naturally variable
annual recruitment. However, given the potential of this method to provide accurate
long-term recruitment data, I believe that it should continue.
A second method of assessing eel populations is currently available; “catch-per-uniteffort” (CPUE). Records of eel catches per net-night have been taken from
commercial fishermen since before the Quota Management System was brought in.
These records are analysed and compared with previous years to provide a model of
eel populations over time. The methodology and latest results of this work (funded by
commercial fishermen) is available in Beentjes and Dunn (2008). The latest CPUE
analyses (Beentjes and Dunn 2008) indicate that eel populations are either stable or
increasing in all Quota Management Areas in the South Island.
This is hardly surprising, as Graynoth et al (2008) found that 49% of longfin eel
stocks are in reserves or in small streams that are unlikely to be fished. This excludes
those waterways upstream of hydro dams. So, if nearly half the waterways are
unfished, what then caused the massive decline in longfin eel populations, and what
are the threats in the future?
Graynoth et al (2008) conclude that hydro dams have reduced eel access to waters that
could support over 6000 tonnes of longfin eels. The average annual commercial
longfin harvest, since the inception of the Quota Management System in 2000, is
approximately 266 tonnes. Given the estimated current national stocks of longfins at
12,000 tonnes (Graynoth et al 2008), and an average annual commercial harvest of
266 tonnes, we can see that the real problem lies with the missing 6000 tonnes of
longfins caused by hydro dams.
Therefore, the decline in longfin eel populations over the last 40 years is likely to
have been caused by exclusion from their habitat by hydro dams. Add the massive
disruption of their habitat through land development and water abstraction, and the
real threats to longfin eels start to clarify. The commercial eel fishery has
correspondingly reduced as a result of these impacts; but to blame commercial fishing
as a principal agent of decline is to misidentify the real threats to the fishery.
Misidentified threats are a triple tragedy for conservation because:
1. The problem does not go away
2. Someone or something else suffers for the sins of others (in this case, commercial
fishermen)
3. The resources spent trying to fix the problem are wasted, and could have been
spent elsewhere to better effect.
It would be easy to make glib statements such as “every time you switch the light on
you are contributing to the problem”. However, the present threat to longfin eels is
that more hydro dams are being proposed on large rivers with unfished catchments
such as the Matiri, Mokihinui and Hurunui Rivers – all which contain high
populations of large longfin eels. Drs Joy and McEwen would do well to divert their
well-intentioned efforts away from banning commercial eel fishing and towards new
hydro dams, water abstraction schemes and water quality issues. By destroying the
sustainable commercial eel fishery they would be destroying the very people with the
most to contribute towards these efforts.
Furthermore, statements that the “inability” of commercial fishermen to catch their
quota provides evidence of declining eel stocks are misguided. Commercial eel
fishermen do not regard their quota as a catch “target”, for the very good reason that
there is no point in catching eels if their commercial return is limited. Landed values
of eels varied over the past 8 years, causing a lower take in some years, in those areas
where commercial eeling is marginal. Other factors governing the take of eels can
include weather conditions (e.g. floods, drought etc), fuel prices, and the full range of
human-induced issues such as access, water quality and water quantity. I suggest Drs
Joy and McEwen read the Eel Fishery Plan for the South Island, undertake a more
detailed review of the scientific literature and consider the risks of misidentified
threats before they continue with their crusade against commercial eel fishers. Perhaps
they could even be persuaded to assist the South Island Eel Industry Association in
our ongoing efforts to maintain sustainable eel fisheries in New Zealand?
Yours faithfully
W.P. Chisholm
CHISHOLM ASSOCIATES
References:
Beaumont, W. R. C.; Taylor, A. A. L.; Lee M. J.; Welton J. S. 2002. Guidelines for
Electric Fishing Best Practice.
Environment Agency R&D Dissemination Centre WRc, Frankland Road, Swindon,
Wilts. R&D Technical Report W2-054/TR.
Beentjes, M.P.; Dunn, A. (2008). CPUE analyses of the South Island commercial
freshwater eel fishery, 1990–91 to 2005–06.
New Zealand Fisheries Assessment Report 2007/08
Chisholm Associates 2009. South Island Eel Industry Association - Eel Fishery Plan
for the South Island. 63pp.
Chisnall, B.L, 1994. An unexploited mixed species eel stock (Anguilla australis and A.
dieffenbachii) in a Waikato pastoral stream, and its modification by fishing pressure.
Conservation Advisory Science Notes No. 69, Department of Conservation, Wellington. 9p.
Graynoth, E.; Jellyman, D.J.; Bonnett, M. (2008). Spawning escapement of female
longfin eels.
New Zealand Fisheries Assessment Report 2008/7. 57 p.