Shetland Shellfish Stock Assessments 2023: A report prepared for the Shetland Shellfish Management Organisation (SSMO)

Leander Harlow, Chevonne Angus, Beth Mouat

Research output: Book/ReportCommissioned report

Abstract

This report details the results of the latest shellfish stocks within the 6nm limit of Shetland alongside management recommendations for the Shetland Shellfish Management Organisation (SSMO). Data in this report originates from landings data supplied by fishermen, catch data from observer trips and age-at-length from market sampling.

Landings per unit effort (LPUE) is used as a proxy for estimating abundance for all species, comparing interannual variation. Where length data is available (brown and velvet crabs), length-based assessments are used to investigate catch composition. Where species can be aged in addition to length data (king scallops), age-length data is examined using virtual population analysis (VPA), allowing each cohort to be tracked throughout the age groups. Additional sampling is carried out to obtain fisheries independent data, such as the biannual scallop survey.

Brown crab LPUE has increased from 2022. However, the west division's LPUE remains below the limit reference point, indicating potential pressure and the requirement for continuous monitoring. Pre-recruit figures suggest potential recruitment concerns, possibly skewed by escape gaps in creels. Anecdotal evidence indicates smaller crabs may remain inshore longer.
The king scallop fishery shows stable LPUE with an upward trajectory above the target reference point. Despite a slight decline in LPUE this year, historical patterns suggest the fishery is being exploited in a sustainable manner.

Velvet crab LPUE has fluctuated between target and limit reference points since 2010. Recent landings and effort declines remain above average. In 2023, LPUE exceeded the target reference point for the first time in nine years, with an increase in pre-recruit size indicating effective management. Additional data from pier-side sampling has contributed to positive trends.

The overall trend in lobster LPUE is increasing and remains above the average of 8.29 kg/100 creels, with the highest LPUE observed around the northern isles. Green crab landings have generally decreased with fluctuations, with effort peaking in 2012 and LPUE stabilizing around 0.2 to 0.3 kg/creel since 2003. The fishery's irregular nature and widespread occurrence of green crabs suggest it has minimal impact on the population.

Queen scallop landings in Shetland have fluctuated between one and 40 tonnes annually, driven by market conditions and irregular fishing, with recent stability but little targeted fishing since 2008. The whelk fishery has fluctuated, with significant landings when local processing was active and recent market opportunities in the Far East. Landings are stabilised around 327 tonnes in 2023, with LPUE showing an increasing trend from 2005, peaking in 2017, and remaining stable since then.

LPUE values for brown crab, velvet crab, and scallops are currently above target reference points, indicating healthy fisheries. As per the SSMO Harvest Control Rules, no immediate management measures are required. Additional effort for Brown crab could be considered,
however this would need to take into consideration lower levels of LPUE in the west region, which is a key area for the targeted fishery. Similarly, new or increased effort for velvet crab in the east region would require scrutiny as LPUE is low. There are no concerns for the lobster, green crab, queen scallop, or common whelk fisheries based on current LPUE values.
Original languageEnglish
Commissioning bodyShetland Shellfish Management Organisation (SSMO)
Number of pages66
Publication statusUnpublished - 1 Aug 2024

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