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.:M98310015 Date:2009/12/7.

An analysis of by-catch in the Icelandic blue whiting fisheryO´ lafur K. Pa´lsson

Curriculum : 981 Seminar

Name : Yun-Ching Chang

School No. : M98310015

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) 1973-2003, international catch by selected ICES area 1973-2002, and total Icelandic catch 1973-2003.

Source: ICES fisheries statistics 1973-2001

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 fi

shery, where the minimum mesh size in the cod end is 13

5-155 mm, depending on fishing area. The meshes get inc

reasingly larger as they are closer to the opening, where t

hey are commonly 64 metres. The opening of the net ca

n be up to 23,000 m2, 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 t

he 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. Si

mple 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

1.

2.

3.

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 - April May June

July August 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 whi

ch 21.1% and 19.1% of the samples, respectively, were positive. For other species t

he frequency of by-catch was less than 6%.

It should be noted that the EEZ split of by-cat

ches 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

Thanks for your attention !