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How the collection of fish length data using electronic monitoring video review measures up to current methods used on a fishery-independent survey

2024; Volume: 55; Linguagem: Inglês

10.2960/j.v55.m746

1813-1859

Lindsey Noel Nelson, David McElroy, Andrew W. Jones, George Maynard,

Marine and fisheries research

Electronic monitoring (EM) systems are tools that can generate fisheries survey data when at-sea challenges such as on-deck logistics, workload capacity, or deployment interruptions prevent staff from fulfilling their duties. We sought to validate EM’s specific utility in collecting fish lengths at a comparable resolution to those collected at sea during a fishery-independent survey, the Gulf of Maine Bottom Longline Survey. We also examined whether measurement accuracy was influenced by tail morphology and length type (fork, total, and stretched total) by selecting individuals from six anatomically variable species. Individuals were measured twice: Survey-based length measurements, LS, were recorded using an electronic measuring board and EM-based length measurements, LE, were visually estimated using a color-coded EM measuring strip during video review. Paired Wilcoxon signed rank tests determined significant differences between the LS and LE distributions for all species overall, and for individual species Atlantic cod, cusk, haddock, and spiny dogfish but not thorny skate or white hake. Kolmogorov-Smirnov tests detected no difference between the distributions of LS and LE, overall and for each species. Examination of the differences between LS and LE for every individual, LD, indicated that the EM-based method slightly over-estimated lengths (μ = 0.89 mm). Linear regression indicated that the effect of extreme small or great lengths on absolute LD was present only for Atlantic cod where LD increased as fish length decreased. Pairwise comparisons of LD among fish length types indicated that fork and stretched total length measurements were overestimated by the EM-based method (μ = 2.39 mm, 3.09 mm, respectively) and this was significantly more than total length (μ = 0.04 mm). We demonstrated that collection of fish lengths using video review could be an adequate substitution for collecting lengths by hand, though it is at the discretion of the end users to determine whether these length differences exceed the acceptable range. These results have particular applications to small scale survey operations, research, and the fishery-dependent sector.