Age, Growth and Reproduction of Dolphin (Coryphaena hippurus) Caught Off the Coast of North Carolina.

Abstract

The common dolphin (Coryphaena hippurus) supports economically important fisheries along the east coast of the United States. In recent years, landings of dolphin from the United States Atlantic have increased dramatically. For example, recreational landings in the US South Atlantic Bight have increased from 162,000 dolphin in the 1960s to over 1.3 million dolphin in recent years. The last age and growth study of North Carolina dolphin was conducted in the early 1960s. It is hypothesized that life history parameters may have changed due to increased exploitation. Age, growth and reproduction were studied on dolphin (n=802; size range=89 to 1451 mm FL) collected between May 2002 and May 2004 from commercial and recreational catches in North Carolina. Annual increments from scales (n=541) and daily increments from sagittal otoliths (n=126) were examined; estimated von Bertalanffy parameters were L∞ = 1299 mm FL and k = 1.08 yr ⁻¹. The maximum age observed was 3 years. No major change in length at age has occurred since the early 1960s. Daily growth increments for age-0 dolphin reduced much of the variability in length-at-age values for age-0 dolphin and provided an average growth rate of 3.78 mm/day in the first six months, which is extremely fast for a teleost fish. Growth of North Carolina dolphin is similar to that found in Florida and the Mediterranean, but differs from observed growth in the Caribbean and Gulf of Mexico. Age at 50% maturity was around 4 months for female dolphin and 6 months for male dolphin. Monthly length-adjusted gonadal weights suggest that peak spawning occurs from April through July off North Carolina; back-calculated hatch dates from age-0 dolphin along with prior studies on the east coast of Florida suggest that dolphin spawning occurs year round with highest levels from January through June. This study provides an updated and improved (year-round sampling and otolith daily ages) age-length function for dolphin caught off the coast of North Carolina using both scale annuli and daily growth increments and provides some of the first comprehensive data on North Carolina dolphin reproduction. The life history of dolphin, including fast growth and early maturity, allows for high levels of exploitation.