A comparison of age- and size-structured assessment models applied to a stock of cisco in Thunder Bay, Ontario

Fisheries Research
By: , and 



Stock assessments are critical to modern fisheries management, supporting the calculation of key reference variables used to make informed management decisions. However, there is still considerable uncertainty as to which class of assessment models is appropriate to use under different circumstances. A common class of models used when age data are available are statistical catch-at-age assessment (SCAA) models, which track annual cohorts through time. When age data are unavailable, as is often the case in invertebrate fisheries where the lack of a bony structure such as otoliths makes aging difficult, statistical catch-at-size assessment (SCSA) models are more often employed, tracking fish or invertebrates through time by size-classes rather than ages. Do SCAA models actually perform better than SCSA models when age data are available, or is this just an assumption we make in fisheries research and management? We examined this question by evaluating the effectiveness of both SCAA and SCSA models in characterizing cisco, Coregonus artedi, population dynamics in Thunder Bay, Ontario. Both models were fit using an integrated framework with multiple sources of data including hydroacoustic estimates of spawning stock, fishery-dependent and -independent age/length compositions, and harvest data. Our results suggest that for cisco in Thunder Bay, data-limitations related to lack of size-composition data over the size range for which cisco growth is rapid resulted in difficulty estimating relative year-class strength within a SCSA. This led to parameter confounding and ultimately the inability to estimate natural mortality within a SCSA. This hampered the utility of a SCSA model in comparison with a SCAA model when age-composition data were available.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title A comparison of age- and size-structured assessment models applied to a stock of cisco in Thunder Bay, Ontario
Series title Fisheries Research
DOI 10.1016/j.fishres.2018.09.014
Volume 209
Year Published 2019
Language English
Publisher Elsevier
Contributing office(s) Great Lakes Science Center
Description 15 p.
First page 86
Last page 100
Country Canada
State Ontario
City Thunder Bay
Other Geospatial Thunder Bay