Shrimp mark-release and port interview sampling survey of shrimp catch and effort with recovery of recaptured tagged shrimp.

Abstract

This report describes the results of two work units conducted under the Shrimp Population Studies in relation to the West Hackberry and Big Hill brine disposal sites. The work units supplemented the historical NMFS efforts for the construction of a Gulf-wide mark-recapture data set as well as the Government's Trip Interview Sampling Survey of shrimp catch and fishing effort. In addition, analyses were conducted on the entire mark-release- recapture data set (1977-1982) to determine rates and functions of growth, mortality and migration of white and brown shrimp. In total 164,217 brown and white shrimp were marked and released. A quality assurance program quantified errors in speciation, sexing and tail length measurement. Short-term (96h) tag-untagged mortality experiments revealed significant tagging mortality; however, the majority of the deaths occurred in the first 48h. A total of 6291 tagged shrimp were recovered and 7042 interviews were conducted in the survey of shrimp catch and fishing effort The nonrecognition and non-reporting of recaptured tagged shrimp, determined through a limited survey, showed that opinions vary substantially among both ports and professions. The introduction of spiked shrimp revealed that non-recognition of tagged shrimp would not seem to be a problem with regard to shrimp house employees. Temporal-spatial patterns of growth, mortality and migration were examined through a reductionist partitioning of the mark-recapture data. Tail length-weight relationships, growth increments and the parameters of the von-Bertalanffy equation incorporating measurement errors were determined. Clear patterns in growth for sex and seasonality were demonstrated for both species. Mortality estimates, that incorporated catch and effort statistics, revealed white shrimp to have a higher natural mortality component than fishing mortality; whereas, brown shrimp seemed to experience approximately equal natural and fishing mortalities. Orientation statistics, a graphical display of density of returns and time at large of tagged shrimp supported the conventional views concerning seasonal movements and migration patterns of the two shrimp species.