A Multi-Species Fishery:
The Shetland Whitefish Fishery
Introduction
This paper summarises information on the catch composition of Shetland whitefish
vessels over the last decade. Over that period, the Shetland whitefish fleet has
varied in size from 20 to 27 vessels (currently 24), most in the size range 20 to 25
metres. The fleet includes seine netters and single and twin-rig demersal trawlers,
and fishes predominantly - although not exclusively - in the waters around Shetland
(the northern North Sea).
Landings by All Shetland Whitefish Vessels
Data
Official records of the weight and value of all landings by Shetland fishing vessels by
species and year (supplied by the Marine Analytical Unit of Marine Scotland
Science). The last year for which these data are available is 2011.
Results
Over the ten years from 2002 to 2011 Shetland whitefish fishing vessels landed at
least 55 individual species of fish (Figure 1). This includes three shellfish species
that are caught by whitefish vessels (Nephrops, squid and cuttlefish). Landings were
also recorded against 10 non-specific groups, including ‘skates & rays’ (which
includes at least four different species) and other mixed or unidentified species.
Eight species accounted for about 90% (by weight) of landings, while the other 47odd species accounted for the remaining 10%.
Of the 55-plus species landed by Shetland whitefish vessels full analytical stock
assessments were available (in 2011) for only six (11%) - cod, haddock, Nephrops,
plaice, saithe & sole.
Ian R. Napier, NAFC Marine Centre, 12th Feb. 2013
Figure 1
Breakdown of the species landed by Shetland whitefish vessels from 2002 to 2011. The weight (bars) and value (line) of each
species as a percentage of the total weight and value of landings by whitefish vessels. Note: there are no zero values on this chartlandings were recorded for all of the species shown.
Ian R. Napier, NAFC Marine Centre, 12th Feb. 2013
Landings by a Single Shetland Whitefish Vessel
Data
Haul-by-haul records of the quantities of retained fish caught by an individual
Shetland whitefish trawler, collated from her skipper’s fishing diaries and other
records. This vessel is considered to be fairly representative of the Shetland
whitefish fleet. She has fished mainly around Shetland for more than a decade, but
has also done some fishing around the Faroe Islands and further south, off NorthEast Scotland (Aberdeenshire).
Results
Total Number of Species Caught
Over the ten years from 2002 to 2011 this vessel recorded landings of at least 26
individual species of fish (Figure 2). Smaller quantities of other species were
recorded as ‘other’ or ‘mixed’ species.
Seven species accounted for about 90% (by weight) of landings, while the other 20plus species accounted for the remaining 10%.
Of the 26 species landed by this vessel full analytical stock assessments were
available (in 2011) for only four (15%) - cod, haddock, plaice & saithe.
Average Number of Species Caught per Haul
Overall the vessel landed an average of just over five (5.2) species per haul, with a
range from zero to 12 species per haul (Figure 3). Three quarters of hauls (73%)
yielded between four and seven landed species, and more than two-thirds of hauls
(69%) yielded more than five landed species.
The average numbers of landed species per haul were very similar around Shetland
(5.2) and Faroe (5.1), although the maximum number per haul around Faroe was
only eight, compared to 12 around Shetland (Figure 4). About three-quarters of hauls
in both areas (73% at Shetland, 78% at Faroe) yielded between four and seven
species.
However, when fishing off North East Scotland the number of landed species caught
per haul was much smaller with an average of only 2.1 and a maximum of five
(Figure 4). Two-thirds (68%) of hauls in this area yielded two landed species or
fewer, compared to only 5% and 7% at Shetland and Faroe respectively. Only 2% of
hauls off North East Scotland yielded more than five hauls.
Ian R. Napier, NAFC Marine Centre, 12th Feb. 2013
In fact a single species - haddock - accounted for 95% of all the landed fish caught
off North-East Scotland, compared to 31% at Shetland and 9% at Faroe (Figure 5).
The largest component of the landed catches at Faroe was Saithe (34%).
Ian R. Napier, NAFC Marine Centre, 12th Feb. 2013
Figure 2
Breakdown of the species landed by a typical Shetland whitefish trawler from 2003 to 2012. The weight of each species as a
percentage of the total weight. Note: landings were recorded for all of the species shown.
Ian R. Napier, NAFC Marine Centre, 12th Feb. 2013
Figure 3
Breakdown of the numbers of landed species caught per haul by a typical
Shetland whitefish trawler from 2003 to 2012. The percentage of hauls with
different numbers of landed species. (Average number of species per haul =
5.21 ± 0.02.)
Figure 4
Breakdown of the numbers of landed species caught per haul in three
different areas by a typical Shetland whitefish trawler from 2003 to 2012.
The percentage of hauls with different numbers of landed species.
(Averages: Shetland = 5.23 ± 0.02, Faroe = 5.15 ± 0.17, NE Scotland = 2.10
± 0.12.)
Ian R. Napier, NAFC Marine Centre, 12th Feb. 2013
Figure 5
Breakdown of the average compositions of catches in three different areas
by a typical Shetland whitefish trawler from 2003 to 2012. The weight of
each species as a percentage of the total weight in each area.
Ian R. Napier, NAFC Marine Centre, 12th Feb. 2013
General Remarks
Shetland whitefish vessels regularly catch and land a large number of different
species of fish.
While about 10 species account for the majority of landings (>90%), up to 50 other
marketable species are landed in smaller quantities.
Many of these are quota species and most are ‘data deficient’. Any of these could
become a ‘choke species’ under a discards ban. That is, a vessel that has expended
its quota of a ‘minor’ species might be prevented from catching its full quota of more
important species.
Some of the species landed in smaller quantities are disproportionately valuable.
Records for an individual Shetland whitefish vessel showed a broadly similar picture
with at least 26 different marketable species recorded, and an average of just over
five species per haul (maximum 12). However, there was a very pronounced
difference in the composition of catches around Shetland and Faroe, and off NorthEast Scotland. Catches in the latter area showed much less variety and were
dominated by a single species (haddock).
This suggests that there can be substantial variations in the characteristics of
demersal fisheries over distances that are not particularly large (the fishing grounds
off North East Scotland are about 150 nautical miles from Shetland). While the catch
of a fishing vessel fishing in one area (such as off North East Scotland) may be
dominated by a single species, the same vessel using the same fishing gear may
have a much more varied catch in another area (such as around Shetland).
The available data, summarised above, are based on quantities of fish that are
landed, and do not include any fish that are discarded at sea. The omission of
discards is unlikely to substantially change the overall picture presented by the
results summarised above. However, this omission could have two effects:
Firstly, it is likely that the range of species being caught is even larger than these
results suggest with some - especially those of limited or no commercial value being discarded at sea.
Secondly, the quantities of some species being landed will not reflect the quantities
actually being caught. Thus the contribution of some species to overall catch
compositions may be greater than the above results suggest. Around Shetland in
Ian R. Napier, NAFC Marine Centre, 12th Feb. 2013
recent years it is likely that this has primarily affected hake; that is, hake probably
accounted for a somewhat greater proportion of fishing vessels’ catches than these
results suggest.
However, neither of these points changes the general picture that whitefish vessels
fishing around Shetland normally catch a relatively large number of species.
Ian R. Napier, NAFC Marine Centre, 12th Feb. 2013