Fish discarded from Scottish demersal vessels: estimators of total discards and annual estimates for targeted gadoids

Y. Stratoudakis, R. J. Fryer, R. M. Cook, G. J. Pierce

Research output: Contribution to journalArticle

61 Citations (Scopus)

Abstract

The main objective of discard sampling programmes is to estimate annual total discards of fish species whose stocks are routinely assessed from catch data. The Scottish discard programme is based on a stratified random design, and a ratio estimator is used to estimate total discards independently in each stratum. Total discards are then estimated by summing across strata. However, the small number of trips that can be sampled by scientific observers from fisheries institutes creates problems with this estimator. Here, a simulated population of fishing trips is used to investigate alternative estimators of total discards for the main fish species (haddock Melanogrammus aeglefinus, whiting - Merlangius merlangus, and cod - Gadus morhua) targeted by Scottish demersal vessels in the North Sea and the West of Scotland. The results show that when the sample size in each stratum is very small, the current methodology - independent ratio estimation in each stratum - can be very biased and imprecise. However, an alternative ratio estimator that relies on a collapsed stratification has negligible bias and greater precision. We use this alternative estimator to estimate total annual discards of haddock, whiting, and cod in the North Sea and West of Scotland from 1988 to 1993.

LanguageEnglish
Pages592-605
Number of pages14
JournalICES Journal of Marine Science
Volume56
Issue number5
DOIs
Publication statusPublished - 1 Oct 1999

Fingerprint

fish discards
whiting
haddock
cod (fish)
North Sea
Scotland
vessel
Merlangius merlangus
Melanogrammus aeglefinus
catch statistics
fish
Gadus morhua
fishing
stratification
fishery
fisheries
sampling
methodology
programme
sea

Keywords

  • discard sampling
  • gadoids
  • ratio estimation
  • Scotland
  • simulation

Cite this

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Fish discarded from Scottish demersal vessels : estimators of total discards and annual estimates for targeted gadoids. / Stratoudakis, Y.; Fryer, R. J.; Cook, R. M.; Pierce, G. J.

In: ICES Journal of Marine Science, Vol. 56, No. 5, 01.10.1999, p. 592-605.

Research output: Contribution to journalArticle

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