Artssammensetning og lengdefordeling i fisket med småmasket trål etter målartene øyepål og kolmule i perioden 2014-2019

Abstract

The purpose of the project was to investigate the species composition and length distribution in the fishery with small-mesh trawl for the target species Norway pout and blue whiting. The Norwegian Directorate of Fisheries (FDir) carried out 9 cruises on 9 different vessels during the years 2014-2019. Six of the vessels fished with small-meshed trawl without grid, and were also rigged to produce fish for human consumption. The remaining vessels fished with small-meshed trawl with grid. Seven cruises were carried out in Norway's economic zone south of 62 N while two cruises were carried out in the EU-zone in the North Sea. On board each of the vessels, generally two trawl hauls were performed per day where each haul lasted from 5 to 7 hrs. It was not trawled at night. On 8 vessels the catches were pumped on board, and on one vessel the catches were lifted on board in sacks. On board the vessels rigged for production of fish to human consumption, this fish was sorted out after the fish from the trawl had been pumped or lifted on board. The industrial fish were transported in gutters or on a conveyor belt to storage tanks with cooled water.

The sampling of industrial fish was carried out by filling 30 l baskets with material from the gutter or conveyor belt from the beginning, middle and end of each trawl haul. Three to six samples were taken from each haul, depending on the quantity in the haul (> 3 samples if the haul was larger than 30 tonnes). The sampled material was sorted to species, family, order or class. Each category was weighed separately to the nearest 1 or 10 g on a Marel 2200 weight. The length of fish species such as Norway pout, blue whiting, silvery pout, herring etc. was measured to the nearest 0.5 cm downwards on a measurement board. Other fish species and invertebrates were measured to the nearest whole cm downwards. Between 10 and 199 individuals of abundant species were measured for length per sample. All individuals of a fish species were measured for length if the number of individuals of that species was ≤ 30 in a sample.

In addition, data from the electronic catch reporting (ERS) and sales notes were used in the further data analyses. FDir registered from 1.1-8.6 times (average: 2.8) as many species/categories in the samples compared with the numbers given in the ERS on the various cruises, and 1.6-8.6 times (average: 3.7) as many species/categories compared with the numbers given in sales notes. A total of 74 different species/categories were registered on all the cruises, while only 23 species categories were given on the nine sales notes from the cruises.

A larger quantity of the target species Norway pout was given in the ERS and on the sales notes on most cruises compared with FDir's results. In total for all cruises, the quantity of Norway pout on the sales notes was 87.3 tonnes higher than FDir's estimate. Estimated percentage of the species group cod, haddock and saithe in storage tanks varied between 0.4 and 2.8% of the quantity on sales notes. In total for all cruises, 12.4 tonnes of these species were missing from the sales notes. In each of the 9 cruises, between 0.5 and 11.3% (0.8-36 tonnes) of the quantity in storage tanks was assigned to an incorrect species in the ERS, and on the sales notes between 1.1 and 12.8% (3,4-41 tonnes) of the quantity was assigned to an incorrect species. The quantity of North Sea herring was clearly underestimated in the ERS and on the sales note on two of the cruises ompared with FDir's estimated quantities. On these two cruises alone, 19 tonnes of herring were missing from the sales notes. In total for all the cruises, 24.7 tonnes of herring were missing on the sales notes. Long rough dab was the most abundant flatfish species on the cruises, but this species was not listed in any of the sales notes. FDir estimated a quantity of 30.1 tonnes of long rough dab missing on the sales notes. On Cruises 2-9, several invertebrate species were registered such as different echinoderms, different species of crustaceans, different species of squid, snails, and polychaetes. Thes categories were mainly not given in sales notes except for northern prawn, Norway lobster and squid on some of the cruises. FDir also registered greater argentine in the samples, and on two of the cruises there were many tonnes of this species in the catches. Greater argentine was always given as argentine in the ERS and on sales notes, and a total estimate of 34 tonnes of greater argentine was missing on the sales notes.

On two of the cruises the total quantities in storage tanks in ERS were 14.1 (34,590 kg) and 11.8% (24,853 kg) higher, respectively, than those in sales notes. On Cruise 1, 21.5% undersized North Sea herring (< 20 cm) was recorded in the catches, which means that the quantity of 29 tonnes of herring is to be regarded as an illegal catch. Almost all cod and most of the haddock and European hake in the samples were smaller than the legal sizes of 40, 31 and 30 cm, respectively. In total for all cruises, it was estimated that 30,825 cod, 61,747 haddock and 80,518 European hake ended in storage tanks. Saithe that ended in storage tanks was mainly larger or equal to the legal size of 40 cm. In total for all the cruises, it was estimated that 14,310 individuals of saithe ended in storage tanks. On the two cruises which were carried out in the EU-zone, a high number of small juveniles of the species Norway pout, cod, haddock, whiting and Euopean hake were recorded in the catches. It was estimated that 4,324 cod, 23,020 haddock, 2.6 million whiting and 18,077 European hake were caught in the catches on these two cruises. The main difference between catches fished with small-meshed trawls with and without grid was that the maximum length of saithe and European hake in the catches was lower in small-meshed trawls with grid than without grid. The maximum lengths of saithe and European hake were 47 and 48 cm with grid and 65 and 62 cm without grid, respectively.