Measuring lumps: Optimising sampling of the commercial landings of lumpfish (Cyclopterus lumpus) in Iceland
Introduction
To aid assessment of an exploited fish stock, it is beneficial to have information on the length, weight and age composition of commercial catches. The gathering of such data can be expensive or logistically challenging because, for example, the boats are at sea for extended periods or the fishery lands the catch over a wide geographical area. It is therefore essential to ensure that when designing a sampling scheme, it can attain a sufficient level of precision in the most efficient way possible.
Lumpfish (Cyclopterus lumpus) are distributed across the north Atlantic and their range extends as far south as the English Channel (Ellis, 2015) and New England in United States of America (Rackovan and Howell, 2017) in the western and eastern Atlantic respectively. In spring and early summer, lumpfish migrate to coastal waters to spawn. In Norway, Iceland, the west coast of Greenland and the east coast of Canada, abundance is high enough to support a directed commercial fishery (Kennedy et al., 2019). In Iceland, there are separate fisheries for the males and females and only the female fishery is considered in the present study. The females are targeted using large mesh bottom set gillnets (267–292 mm), which are laid in shallow (< 40 m depth) coastal areas. The female lumpfish fishery is primarily a roe fishery, and the carcass has lower value per kg than the roe. Thus, when space is limiting, there is little incentive to land the whole fish and the roe is removed at sea.
Female lumpfish are exclusively targeted by small boats where fishing trips are < 1 day (Kennedy et al., 2019). Many of these boats are based in small communities far from major population centres. For example, the Norwegian fishery primarily takes place in the northern region and the Greenland fishery takes place along a 1600 km coastline with limited infrastructure. In addition, the Greenland fishery is carried out using small open boats, with little extra space for the storage of ungutted fish. With the combination of remoteness and limited space, it can be time-consuming and expensive for personnel to reach areas where the fishing boats are based and whole fish rarely reach processing facilities, thus, biological measurements cannot be taken.
In Iceland in 2012, it became mandatory to land lumpfish carcasses. The roe could still be removed at sea as long as both the roe and carcass were landed. The proportion of landings consisting of ungutted lumpfish gradually rose from 77% in 2012 to 100% in 2017 (MFRI, 2021). The industry has also shifted from fishers salting and selling their own roe or commissioning a company to do it on their behalf, to fishermen selling the whole fish to roe processors. The result of this is that whole fish from a wide geographical area are concentrated in a small number of locations and many fish can be measured from many boats.
The sampling of lumpfish from commercial catches began in 2008 in a collaboration between BIOPOL (Iceland) and the Marine and Freshwater Research Institute (Iceland). This initially began as personnel accompanying the fishers on fishing trips and measuring large numbers of fish. It would therefore take one day to sample one boat, but many fish could be sampled. However, for other species, measuring many individuals from a single day is of limited value (Helle and Pennington, 2004). Given the change in the lumpfish industry due to the change in the regulations, the sampling regime moved from sampling aboard boats to sampling at the roe processors. The lumpfish fishery in Iceland takes place all around the coast with the exception of the southern coast (Fig. 1). There are seven management areas and boats select a management area for the current season and cannot fish in more than one area. Area B is divided into two areas with area B2 opening later than area B due to issues with bycatch of birds.
The aim of this study is to assess the precision of the current lumpfish sampling scheme in Iceland and identify areas for improvement. Specific questions include whether the timing of the sampling within the season or the landing location has an impact on length measurements, how many boats and how many fish from each boat need to be sampled and what is the effect of storage on weight of the fish. Given the hindrances encountered in the sampling of commercial catches of lumpfish, this analysis of the Icelandic sampling scheme provides valuable information in which to base future sampling schemes in other lumpfish fisheries.
Section snippets
Sampling
Length and weight data of lumpfish from the commercial fishery (Table 1) are collected by the Marine and Freshwater Research Institute (MFRI) and BioPol in Iceland periodically throughout the fishing season (late March to early August, exact dates vary between years). Sampling is carried out at factories processing the roe and also at harbours where the fish is landed. In the factories, the fish are stored on ice in a temperature-controlled room until processing and are labelled with the boat
Results
Lumpfish landed by the commercial fishery fell into a narrow unimodal length distribution (Fig. 2) with 95% of the raw length measurements falling between 36 and 47 cm (mean = 40.9) and 95% of the weight measurements falling between 1966 and 4420 g (mean = 3003 g).
Regarding variation in length, the effect of area was significant (Table 2) with a consistently greater length in Faxaflói compared to the north coast with an average difference of 2 cm (Fig. 2). This was also true of weight, with an
Discussion
Lumpfish show limited variation in mean length between samples from the same boat, between different boats, between areas and between years. This limited variation is likely due to a combination of the fishing pattern and gear used by individual boats and the life history of this species. In the female lumpfish fishery, individual boats tend to lay their nets at the start of their fishing period and haul them periodically (approximately every 3–4 days) and then set them out again close to where
Funding
This work was funded by the Marine and Freshwater Research Institute (Iceland) and BioPol (Iceland).
CRediT authorship contribution statement
James Kennedy: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Resources, Writing – original draft, Writing – review & editing, Visualization, Supervision, Project administration, Funding acquisition.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The author's appreciation goes out to the fishers that allowed their catch to be measured, the fishing companies that accommodated us and allowed us access to their factories, and of course, to the teams of people who travelled around Iceland to perform the measurements. The author would like to thank two anonymous reviewers for their helpful comments on an earlier version of the manuscript. The author would also like to acknowledge the great Icelandic landscape which made travelling around
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