Validated age and growth estimates for Carcharhinus obscurus in the northwestern Atlantic Ocean, with pre- and post management growth comparisons

This paper is not subject to U.S. copyright. The definitive version was published in Environmental Biology of Fishes 97 (2014): 881-896, doi:10.1007/s10641-013-0189-4.Age and growth estimates for the dusky shark, Carcharhinus obscurus, were derived from vertebral centra collected in the northwestern Atlantic Ocean. Sample collection spanned the years prior to and following the implementation of management measures (1963–2010). Growth was compared pre- and post- population depletion and pre- and post- management to investigate the possibility of density-mediated shifts in age and growth parameters over time. There was no evidence of difference between periods for either sex. Additionally, bomb radiocarbon dating was used to determine the periodicity of band pair formation. Results support the traditional interpretation of annual band pairs up to approximately 11 years of age. After this time, vertebral counts considerably underestimate true age. Maximum validated ages were estimated to be between 38 and 42 years of age (an increase of 15 to 19 years over the band count estimates), confirming longevity to at least 42 years of age. Growth curves estimated using only validated data were compared to those generated using band pair counts. Logistic growth parameters derived from validated vertebral length-at-age data were L ∞  = 261.5 cm FL, L o  = 85.5 cm, t o  = 4.89 year and g = 0.15 year−1 for the sexes combined. Revised estimates of age at maturity were 17.4 years for males and 17.6 years for females

Discard Estimates from Self-Reported Catch Data: an Example from the U.S. Northeast Shelf

<p>Discarded catch can account for a significant amount of fishing mortality and can be a major source of uncertainty when calculating total removals for stock assessments and management. Observers provide estimates on the types and quantity of fish that are caught, but observer coverage of a fleet can often vary directly with funding. On the Northeast U.S. shelf, the Northeast Fisheries Observer Program (NEFOP) has collected data on catch and discards for assessment and management purposes since 1989. The Cooperative Research Study Fleet (hereafter “Study Fleet”), working with the Northeast Fisheries Science Center, collects self-reported catch and discards from commercial vessels; however, the Study Fleet program was not developed as an observer program, and these data are not used for management. The number of vessels reporting data in the Study Fleet program is much smaller than the total number of vessels recorded through the observer program (NEFOP plus the At-Sea Monitoring Program), and unlike the observer program, the Study Fleet program is not conducted within a statistically designed sampling program. We compared observer and Study Fleet data for six species collected with otter trawls from 2007 to 2014 to determine whether the reported kept catch and discard values and the total estimated discards from the two programs were similar. In general, the estimates of catch and discards were similar, but due to the large number of samples, significant differences were discernible. Of the 20 comparisons of total estimated discards between the two programs, 13 had similar magnitudes and trends, 4 had similar trends with different magnitudes, and 3 were not similar. Our results indicate that for the subset of species and gear tested, the fishing industry has the capacity to accurately self-report information. With a rigorous quality control program, including appropriate audit and compliance checks to ensure confidence in the data, programs collecting self-reported information for assessment and management may be possible in the future.</p> <p>Received October 14, 2016; accepted May 26, 2017Published online September 5, 2017</p