DOI: 10.5285/fd2f9f1c-bb9f-484e-bbc1-b3d20668b8d2
title: Patagonian toothfish (Dissostichus eleginoides) catch and size-distribution data from the South Georgia (southwest Atlantic) groundfish survey, 1986-2023

description: This submission contains information on catch and size-frequencies of Patagonian toothfish (Dissostichus eleginoides) from the South Georgia groundfish survey, collected during scientific trawl surveys from 1986 to 2023. These data were primarily collected to produce estimates of Patagonian toothfish biomass and recruitment (Shag Rocks), to support the management of the Patagonian toothfish fishery and to improve understanding of the biology and ecology of Patagonian toothfish. Data were primarily collected by Martin A. Collins, Mark Belchier, Inigo Everson, Jude Brown, Phil Hollyman, Simeon Hill, Tom Marlow, Caradoc Jones, Rebecca Mitchell & Sue Gregory.

Since 1990, the South Georgia groundfish surveys were funded by the Government of South Georgia and the South Sandwich Islands. Earlier surveys were funded by the US and Polish governments.
description: Trawl surveys
Data on the abundance and distribution of Dissostichus eleginoides were collected during 28 demersal trawl surveys conducted primarily during the austral summer (Nov - Feb) at South Georgia and Shag Rocks, between 1987 and 2023. The survey design has remained constant throughout the time series despite changes in survey vessel. From the 1991 survey onwards, gear was standardized (commercial sized otter trawl FP-120, wingspread 18-20 m, headline height 3-6 m, cod end mesh 40 mm). Before this, broadly similar gear was used on each of the early surveys (Belchier et al., 2015). 30-minute trawls at a speed of 3-4 knots were carried out in a random-stratified design split into five sectors consisting of Shag Rocks and the South Georgia shelf, divided into northwest, northeast, southwest, and southeast quadrants, and two depth zones (depth zone 1: 100-200 m; depth zone 2: 201-350 m). The trawl dataset also contains data from winter surveys, performed using the standard survey design but in April/May (2008 and 2021) or September (1997 and 2007), and dedicated deepwater surveys. 
During each survey, the total catch (recorded as number of individuals and total catch weight in kg) of D. eleginoides per trawl was recorded along with information on trawl location, time, depth, and trawl characteristics (trawl duration, distance trawled, horizontal and vertical net opening). Catch number (total number of individuals) was used to calculate size-specific catch for each of six size classes (&lt; 26 cm, 26-37 cm, 38-47 cm, 48-57 cm, 57-66 cm, &gt; 66 cm) based on the observed proportion of fish in each size class from the size-frequency data (see below). Size-frequency data were either used to directly assign counts to each size-class (trawls in which all captured toothfish were measured), or via multiplication of the total catch number with the proportion of measured fish belonging to each size-class (trawls in which only a sub-sample of toothfish were measured) and subsequently rounded to the nearest integer.

Size data
In the majority of trawls, all D. eleginoides captured were measured (Total length: snout to the end of the caudal fin, cm), producing the associated dataset. In the small proportion of trawls containing many D. eleginoides, captured individuals were sub-sampled at random and measured to provide a representative sample of the size-distribution of toothfish in that trawl.
description: All data processing and cleaning were performed in R version 4.3.3 (R Core Team 2024).
description: Raw trawl data were cleaned to remove trawls hauled early due to unsuitable ground, and those that were deemed unrepresentative due to gear failure.