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Fisheries

One fish, two fish, small fish- don’t fish!

Björnsson, B., Sólmundsson, J.,and Pálsson, Ó . K. Can permanent closures of nearshore areas reduce the proportions of undersized fish in the Icelandic longline fishery? – ICES Journal of Marine Science, doi: 10.1093/icesjms/fsu162.

 

Introduction

Issues of overfishing concern seafood eaters, fishermen and fishery managers. Humans exploit fish and aquatic invertebrates from all bodies of water for food. Fishery restrictions and conservation strategies are in place to protect current stocks, increase depleted populations and to attempt to guarantee a future with healthy fisheries.

A common fishery management technique uses the size of the animal to determine legal catch restrictions. Organisms that are too large are assumed to contribute disproportionately to reproduction of the species whereas individuals that are too small may not have had a chance to breed yet. Iceland’s economy relies heavily on the fishing industry and protecting popular fish species helps ensure a healthy economy in the future. The Icelandic cod fishery restricts catch of small and large size classes. The fishery also enforces prohibition of certain gear (i.e. purse seines), a quota system for fishermen, and fishery closures during spawning times.

Cod drying racks in Flateyri, Iceland. photo credit: Maya

Cod drying racks in Flateyri, Iceland. photo credit: Maya

Longline fishing causes less damage to the physical ecosystem than trawling and is less energy intensive, but the bycatch can be significant- including fish of the target species that are too large or too small. In Iceland the regulatory government body closes fishery areas at times of high juvenile abundances in an attempt to lessen the burden on small, not yet sexually mature individuals of important commercial fishery species.   This paper aims to find areas of high juvenile abundance of cod and haddock and to investigate the possible scenario of permanent fishery closures in these important nursery grounds.

Methods

 The analyses in this paper were based on government longline fishery inspection data with over 500,000 fish measured. Each sample had an associated date, geolocation, depth and fish length. Distance from shore was calculated from each longline location as well as from fishery closure location.

 

Results 

During the study years (2005-2013), 75% of longline catches of cod, haddock and wolffish occurred less than 30 km from shore, 41% within 10 km. Cod were found in more areas and also showed more areas with high juvenile and young fish abundance. Overall the percentage of undersized cod decreased with depth and distance from shore. About half of the fishery closures due to high numbers of undersized cod or haddock were within 10 km of shore. The average size of a fishery closure was about 100 square km, less than 0.1% of the cod fishing area around Iceland.

 

Lengthdistributionofcodcapturedinthelonglinefisheryin Icelandic waters during 2005 – 2013 according to distance from shore: (a) ,5, (b) 5–10, (c) 10–20, (d) 20–30, (e) 30–40, (f) 40–80, and (g) .80 km. Percentage of fish ,55 cm is indicated. All measurements were made by observers on-board vessels. Total number of length measurements was 301 741.

Lengthdistributionofcodcapturedinthelonglinefisheryin Icelandic waters during 2005 – 2013 according to distance from shore: (a) ,5, (b) 5–10, (c) 10–20, (d) 20–30, (e) 30–40, (f) 40–80, and (g) .80 km. Percentage of fish ,55 cm is indicated. All measurements were made by observers on-board vessels. Total number of length measurements was 301 741.

 

 Location of annual fish catches (tonnes per nautical square mile) in the Icelandic longline fishery during 2005 – 2012, (a) cod, (b) haddock, and (c) wolffish. Depth contours at 100, 200, and 500 m.

Location of annual fish catches (tonnes per nautical square mile) in the Icelandic longline fishery during 2005 – 2012, (a) cod,
(b) haddock, and (c) wolffish. Depth contours at 100, 200, and 500 m.

 

Cod, haddock and wolfish are the three species of greatest importance and abundance in the Icelandic longline fishery. In the 10 km closest to shore these three species constituted 94% of the total longline catch. The highest proportion of undersized cod were caught using handline and longline fishing gear compared to trawl and bottom seine nets.

Significance

Fishery closures based on distance from shore are far easier to implement and enforce than restrictions based on depth, although this study showed a clear relationship with more undersized fish abundance at shallower depths. Over the study area, within 10 km of shore the average number of undersized cod exceeded 25%, the number used in Iceland to enact temporary fishery closures.

Over the last 35 years longline use in Icelandic waters has increased dramatically, its relative proportion tripling compared to other fishery methods. Currently temporary, localized closures are used as the need appears but are only in place two weeks before the areas automatically return to normal fishing regulations.

The authors of this study suggest that the current system for short term, small closures is not sufficient to protect the widespread undersized fish. However, based on the importance of near shore habitats as nursery grounds more permanent closures in all or some principal areas could be more effective in protecting young fish until they reach maturity and travel further offshore.

The fishing industry and fish populations are dynamic, changing with fishing technology, season, and weather. Continuous monitoring and adaptive management are the best hope of successful management practices.

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