An analysis of by-catch in the Icelandic blue whiting fishery O´ lafur K. Pa´lsson Curriculum:981 Seminar Name:Yun-Ching Chang School No.:M Date:2009/12/7 Marine Research Institute, P.O. Box 1390, 121 Reykjav´ık, Iceland Received 28 June 2004; received in revised form 14 December 2004; accepted 18 December 2004

Introduction - Blue whiting (Micromesistius poutassou) Actinopterygii Gadiformes Gadidae Classification : Biological features: Spawning grounds Feeding grounds

Total international catch of blue whiting (Micromesistius pautassou) , international catch by selected ICES area , and total Icelandic catch Source: ICES fisheries statistics ICES Fishing area Feeding ground Spawning ground

Fishing Gear: Mid-water trawls of Iceland  Gloria mid-water trawls  Fishing grounds of blue whiting in Iceland Iceland It operates without touching the bottom and is frequently trawled at depths of a few hundred metres in the redfish fishery, where the minimum mesh size in the cod end is mm, depending on fishing area. The meshes get increasingly larger as they are closer to the opening, where they are commonly 64 metres. The opening of the net can be up to 23,000 m 2, the size of 5 football fields.

Characters of blue whiting fishery in Iceland  The Icelandic blue whiting fishery is a highly modernized one, capable of locating, catching and landing large amounts of fish within a short period of time.  Hidden mortality in fisheries may appear in many different forms, such as accidental by-catch in a given fishery. In recent years, concerns have been raised as to the potential by-catch in modern pelagic trawl fisheries and its effect on the fish stocks subjected to the by-catch.  Why do this research? Reasons and Goals ?

The alternative possibility is to sample the catch during landing. This approach enables relatively easy access to the catch, and a convenient setup for the subsequent handling of the samples for specific measurements. Materials and methods – Sampling sites  Sampling sites of Iceland Trips for sampling were planned to be selected randomly from the operating fleet, consisting of 21 vessels.

From the first 1,000 t of a catch, one sample was taken per 100 t, on average. From the part of a catch in excess of 1,000 t one sample was taken per 200 t on average, or a maximum of five samples. Materials and methods – Number of samples The total weight of the sample was measured. The planned weight of a sample was approximately 500 kg, but most samples were 400–600 kg. By-catch rate (%) was calculated as weight of by-catch species per 100 kg of catch. Simple t-test was used to calculate confidence intervals.  Fishing boat of mid-water trawl in Iceland

Blue whiting catch and effort of the Icelandic fleet, and sampling intensity in the by-catch programme by months 2003, showing sampling operations (lines 1–3) and operations of the fleet (lines 4–6)

Results Frequency and quantity Spatial and seasonal distribution Length distribution By-catch analysis

Frequency distribution of by-catch by numbers in samples in the Icelandic blue whiting fishery 2003 Cycloperus lumpus Pollachius virens Argentina silus Gadus morhua

Results of by-catch analysis, showing sample level figures, by- catch values by weight and numbers raised to total catch weight, and by-catch rate (% weight)

Variability in by-catch among and within trips, using ANOVA with fish numbers per trip as response and trip as factor

Topographic chart around Iceland and Faroese waters

Geographic positions of sampled hauls and all hauls of the Icelandic blue whiting fleet 2003 March - AprilMay June JulyAugust September - December Source: log-book database of the Marine Research Institute

Spatial distribution of saithe (Pollachius virens) by-catch rates (%) in hauls of sampled trips 2003 May - June July August September - November

Spatial distribution of silver smelt (Argentina silus) by-catch rates (%) in hauls of sampled trips 2003 May - June July August September - November

Spatial distribution of cod (Gadus morhua) by-catch rates (%) in hauls of sampled trips 2003 May - June July August September - November

Spatial distribution of lumpsucker (Cyclopterus lumpus) by-catch rates (%) in hauls of sampled trips 2003 May - June July August September - November

Division of by-catch in the Icelandic blue whiting fishery between the EEZs of Iceland and Faroes

Length distributions (numbers) of by-catch species in the Icelandic blue whiting fishery 2003 Pollachius virens Gadus morhua Sebastes marinus Argentina silus Cycloperus lumpus Sebastes mentella

Discussion – By-catch rate, frequency and distribution  The highest frequency of by-catch was observed for saithe and silver smelt, for which 21.1% and 19.1% of the samples, respectively, were positive. For other species the frequency of by-catch was less than 6%.  It should be noted that the EEZ split of by- catches is hardly more than an approximation to a real spatial separation of the stocks.  Relationships between by-catches and catches.

 The most feasible way to reduce the by-catch is to mount size selective sorting grids on the trawls that sort larger fish out of the trawl, but retain smaller sized fish as the target species.  Considering the huge size of the gear used and the great amount of the target species caught, the frequency and quantity of by-catch appears in fact rather low. Discussion – Fishing gear for reducing the by-catch

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