Change-in-Ratio and Index-Removal Methods for Population Assessment and Their Application to Snow Crab (Chionoecetes opilio)

Abstract

1993. Change-in-ratio and index-removal methods for population assessment and their application to snow crab (Cbaionoecetes opilio). Can. J. Fish. Aquat. Sci. 50: 1467-1496 Change-in-ratio and index-removal estimators are presented in a general form suitable for fisheries studies of closed populations. We also show how to combine the two approaches in a single estimator. In order to use these methods, it is necessary to sample the population before and after the fishery and to determine the total harvest and its composition. We used the methods to estimate the population of legal-size snow crab (Claionoecetes opiliu) in St. Mary's Bay, Newfoundland, before and after the fishery and to estimate the catchability coefficient and exploitation rate. It is also possible to estimate the abundance of prerecruits but this requires the assumption of equal catchability of ail anirnals, a condition that may not be met. These methods have been largely neglected by fishery scientists; however, they seem to be ideally suited for studies of many temperate popultttions of large sedentary crustaceans, particularly those subjected to fisheries of short duration.Des estimateurs des changements dans les proportions et le prdevernent sont present& sous une forme g6nerale qui se prGte aux etudes d'halieutique de populations fermees. Nous montrons aussi comment combiner les deux apprsches en un estimateur unique. Afin d'utiliser ces methodes, i 0 est necessaire d'echantillonner la population avant et apres la peche, et de determiner la recolte totale ainsi que sa composition. Nous avons appliqu6 ces rnethodes 2 I'estimation de la population d a m crabe des neiges de taille legale (Chionoecetes opilio) dans la baie St. Mary's, Terre-Neuve, avant et aprPs la g@che, et nous les avons applicguees 2 I'estimation d u coefficient du potentiel de capture ainsi que du taux d'exploitation. II est egalement possible d'estimer ['abondance des jeunes qui ne sont pas encore recrutes, mais pour cela, i B faut adopter I'hypothGse selon laquelle tous les sujets sont egasernent sujets A Gtre captures, ce qui peut se reveler inexact. Ces mkthodes ont kt6 largemen! negligees par les spt5cialistes des pGcl~es; toutefois, elles semblent convenir parfaitement aux 6tudes de bon nombre de populations en none ternperee de gros cru~taces sedentaires, particuli6rernent ceux qui font l'sbjet d'une p@che de courte durke.

Methods for stock assessment of crustacean fisheries

“…Dawe et al, 1993;Chen et al, 1998;Frusher et al, 1998) and CIR has similarities with depletion methods. The method works by dividing the population into two distinct components and observing the change in their ratio following a known removal of animals.…”

“…Eberhardt (1982) and Dawe et al (1993) recognised the importance of replicate CPUE samples for estimation of empirical variances of the component proportions. The population is assumed closed or factors affecting the population (migration, natural mortality, etc.)…”

“…Relative catchability of the two components is assumed to be constant, although actual catchability can change between episodes. The method has recently been applied to a range of crustacean stocks, including Homarus americanus (Comeau and Mallet, 2001), Pandalus platyceros (Bishop et al, 2000) and Chionoecetes opilio (Dawe et al, 1993;Chen et al, 1998).…”

Criteria for Determining Maturity Stage in Female American Shad, Alosa Sapidissima, and a Proposed Reproductive Cycle.

“…If the harvest is also known, then the size of the run can also be estimated. These methods are described by and have been used by DAWE, HOENIG and XU (1993).…”

Monitoring marine populations and communities: methods dealing with imperfect detectability

“…for many temperate populations of large sedentary crustaceans, particularly those subjected to fisheries of short duration (e.g. Dawe et al 1993, Frusher et al 2007). …”