Multiple techniques for determining stock relationships between orange roughy, Hoplostethus atlanticus, fisheries in the eastern Tasman Sea

Abstract

Five techniques were used to determine stock relationships between four spatially isolated but geographically close orange roughy fisheries in the eastern Tasman Sea: the Lord Howe Rise (HOWE), Northwest Challenger (NWCH), Southwest Challenger (SWCH), and Westpac Bank (WPAC). The techniques included life history traits (age and length at maturity), population length frequency analysis, otolith shape analysis, genetic makers, and a comparison of spawning times. The estimated ages and lengths at onset of maturity did not identify clear stock differences between the four areas. Otolith shape revealed two groups: HOWE/NWCH and SWCH/WPAC. There were significant size differences between HOWE and NWCH (and between HOWE–SWCH and HOWE–WPAC) with larger fish on HOWE. One out of six nuclear DNA markers revealed significant heterogeneity among sites. Mitochondrial DNA polymorphisms of the control region revealed no heterogeneity among areas, but restriction digests of the whole mitochondrial genome revealed differences between HOWE and NWCH/SWCH. There was considerable between-year variation in the time of the onset of spawning at SWCH (3 weeks) and WPAC (4 weeks). In both areas, the time of spawning was later in the early 1990s than in the late 1990s. No major oceanographic features that might isolate stocks were identified in this region of the Tasman Sea. The biological differences between orange roughy taken from HOWE, NWCH, and SWCH indicate that these fisheries could be managed as independent stocks. There were no biological differences between SWCH and WPAC and these fisheries probably exploit one straddling stock.