Alaska Fisheries Interaction Team Pacific Cod Maturity Study

Pacific cod researcher.

Knowledge of spawning aggregation processes provides valuable insight for fisheries investigations. Important information such as spawning location, duration, and seasonality require knowledge of the gonad developmental stages of individual fish.  Investigations of these processes for Pacific cod require a quick and easily applicable tool, allowing for the large sample sizes and broad application necessary for such a wide-ranging species. A visual staging key based on the external and internal appearance of gonads can be applied inexpensively to obtain large sample sizes over a range of collection platforms. Though easily applicable, visual staging keys may provide subjective and often inaccurate data, especially for gonads in transitional stages of development. In this research, histological assessments will be used to verify visual keys. Cell structural changes corresponding to advancement in gonad maturity will be identified through histological assessment and compared to gross visual changes observed in gonads. 

Key Development

With minimal literature available on Pacific spawning aggregations in the Bering Sea, FIT investigators initially employed a combination of maturity stages documented in the literature. With continued observation of the visual changes which occur in gonad maturation during the spawning season, a more descriptive key was developed. Histological specimens were collected along with visual staging data and are now available for comparison. Preliminary analysis of the 2003 specimens indicates that the gross visual key is adequate in grouping advancing levels of maturity throughout the spawning season. 

Observer Project Implementation

The Fisheries Monitoring and Analysis Division of the AFSC monitors groundfish fishing activities in the Bering Sea and provides an opportunity to collect data through fishery effort from a greater space and time range than available to FIT scientists. Early versions of the Pacific cod maturity key were provided to Observers assigned to various vessels and processing plants.  Observers responded positively collecting large amounts of data from a wide range of vessel and gear types. 

Examination of Classification Errors

Histological specimens have been collected during FIT cod cruises from 2003 to 2005. Maturity stages were coded corresponding to the maturity key for specimens and many have associated photographs and written descriptions. Processing and analysis of these specimens will allow for the fine tuning the cod maturity key, or will provide evidence needed to combine stages due to lack of clarifying structures.