File Report, Pink Shrimp Fecundity Studies

Identification Information

Citation

Originator: Hannah, Robert W.

Publish Date: 1991

Online Link: None

BPA Project #:

Contact Information

Agency: Oregon Department of Fish and Wildlife

Name: Cedric Cooney

Job Position: Natural Resources Data and Systems Manager

Telephone: 503-947-6094

E-Mail Address: cedric.x.cooney@odfw.oregon.gov

Description

Abstract: Maintaining an adequate level of parent stock to ensure future recruitment is, perhaps, the primary goal of fishery management. Ultimately, this endeavor is actually aimed at maintaining the reproductive output of the stock, more appropriately expressed in terms of the production of viable eggs or larvae. To accomplish this goal, managers need to know not only how fishing influences the adult spawning stock, but also about effects on sex composition of the population, age-specific average fecundity, and egg size or larval condition. In the case of pink shrimp (Pandalus jordani), we have crude estimates of the spawning stock. We also have sex composition estimates that are accurate enough to show that these protandric hermaphrodites are very effective at altering the age of sex change, subsequently achieving a roughly balanced sex composition in most years (Charnov et al 1976, Hannah and Jones 1991). This capacity is very impressive, considering that the stock experiences heavy, size-selective fishing pressure. Unfortunately, much less is known about how various levels of spawning stock translate into actual total reproductive output for pink shrimp. Some work was done in the early years of the fishery to characterize the basic fecundity of pink shrimp. Dahlstrom (1970) presents data from 1964 on the length-fecundity relationship for pink shrimp from northern California, and also asserts that there is no relationship between egg size and carapace length for pink shrimp. A limited amount of data on the length-fecundity relationship is also available from Oregon waters (ODFW unpublished data). While this early data seems to be of high quality, it suffers from several shortcomings when applied to the present day shrimp population. Frist, overall sample sizes were fairly small, the largest single sample being from only 62 shrimp, with other samples being much smaller. Second, the early samples were almost exclusively age 2 and older shrimp, while the modern day spawning population is composed of a large percentage of age one females. A third problem is that age-specific mean lengths are quite variable and have increased since the early years of the fishery (Hannah and Jones 1991), raising two important questions. First, what effect have changes in growth had on the length-fecundity relationship? Also, when growth is highly variable, how useful is an "average" age-specific fecundity in estimating reproductive output of the stock? To fully describe the factors effecting variability in the reproductive output of pink shrimp will probably take a long time and require analysis of samples from a wide variety of locations and years. To begin chipping away at this task, in 1989 we began collecting and analyzing samples of egg-bearing pink shrimp as opportunity allowed. This report summarizes progress to date in our ongoing study of the fecundity of pink shrimp.

Purpose:

Time Period of Content: 1989 and 1990

Geographic Extent: Oregon

Status: Final

Use Constraints:

Format: PDF

Data Quality Information

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Data Information

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Is a physical copy maintained for reference at Headquarters? Unknown