Discovery, evaluation, and implications of blue crab, Callinectes sapidus, spawning, hatching, and foraging grounds in federal (US) waters offshore of Louisiana

Abstract

Although blue crabs, Callinectes sapidus Rathbun, 1896, are ecologically important predators and support the world's most valuable crab fishery, little is known about their spawning and hatching migrations beyond the estuary. We discovered unexpectedly high concentrations of female blue crabs actively spawning, hatching their eggs, and foraging in federal waters within our study area, the Ship, Trinity, Tiger Shoal Complex (STTSC) ≥ 20 km off the Louisiana coast. During a three-year investigation, blue crab abundances were significantly higher on Ship and Trinity Shoals than the surrounding, muddy and deeper seafloor. Crabs from the STTSC compared favorably with those from nationally recognized spawning grounds in terms of condition factor (an index of health), fecundity, and abundance. Ninety percent of females possessed a sponge, large ovary, or both. Eighty-seven percent of non-ovigerous females showed evidence of a previous hatching. An analysis of ovarian development suggests that STTSC crabs produce new sponges approximately every 21 d, and at least seven broods per spawning season (̃April- October). Monthly declines in sponge weight and a companion study of benthic macrofauna suggest fecundity may be limited by food supply in areas of high crab abundance. Symbionts did not negatively impact condition factor. Carapace width including the lateral spines was a much poorer estimator of crab weight than carapace width excluding the lateral spines, height, length, or estimated volume. Given the increasing national importance of the Louisiana blue crab fishery and declines elsewhere, we recommend that management safeguard these previously unknown spawning, hatching, and foraging grounds. © 2009 Rosenstiel School of Marine and Atmospheric Science of the University of Miami.