Life history, population dynamics and yield-per-recruit modeling of Atlantic croaker, Micropogonias undulatus, in the Chesapeake Bay area

Otoliths, scales, dorsal spines, and pectoral fin rays, of Atlantic croaker, Micropogonias undulatus, were compared for legibility of presumed annuli and precision in repeated readings, to determine the best structure for ageing. Marks on transverse otolith sections were easiest to read and showed the best agreement between readings. Fish collected in Chesapeake Bay and in Virginia and North Carolina coastal waters during 1988-1991 were then aged using otolith sections. Ages 1-8 were recorded, but eight-year-old fish were rare. Marginal increment analysis showed that for ages 1-7 annuli are formed once a year during the period April-May. Otolith age readings were very precise, with percent agreement within and between readers greater than 99%. Observed lengths-at-age were highly variable and showed a rapid decrease in growth after the first year. Observed lengths for ages 1-7 showed a very good fit to the von Bertalanffy growth model (r&\sp2& = 0.99; n = 753). No differences were found between sexes. Total annual instantaneous mortality (Z) ranged from 0.55 to 0.63. Atlantic croaker are multiple spawners with indeterminate fecundity. Mean length at first maturity for males and females was 182 and 173 mm TL, respectively. More than 85% of both sexes were mature by the end of their first year and all were mature by age 2. Spawning extends over a protracted period (July-December), but individual fish spawns for only 2-3 months. Spawning starts in Chesapeake Bay and continues offshore and south as Atlantic croaker migrate from the estuary. Seasonal fluctuations in sex ratios suggest that males start leaving the estuary earlier than females. A high incidence of atretic advanced yolked oocytes in spawning females suggests that a surplus production of yolked oocytes is part of Atlantic croaker reproductive strategy. Yield-per-recruit modeling results indicated that, over a likely range on natural mortality values, present levels of harvest in Chesapeake Bay are below the maximum potential yield-per-recruit. Results from this study do not indicate the existence of a group of larger, older fish in the Chesapeake Bay region and suggest that the hypothesis of a different population dynamics pattern for Atlantic croaker north and south of North Carolina, should be reevaluated

Age And Growth Of Weakfish, Cynoscion Regalis, In The Chesapeake Bay-Region With A Discussion Of Historical Changes In Maximum Size

Weakfish, Cynoscion regalis, were collected in 1989-93 from commercial catches in the Chesapeake Bay region, and special collections of large fish were made in Delaware Bay. Ages were based on sectioned otoliths. Most weakfish were 200-600 mm TL and ages 1-4 years. Maximum age was 17 years from a 1985 Delaware Bay fish. Maximum current observed ages were 12 years in Chesapeake Bay and 11 years in Delaware Bay. However, fish older than age 6 were rare in both areas. There was no evidence that Delaware Bay fish reached a larger maximum size or maximum age than Chesapeake Bay fish. Although weakfish size was a poor predictor of age, weakfish growth was well described by the von Bertalanffy growth model (r(2)=0.98, n=854). Maximum size and age has fluctuated in both Chesapeake and Delaware Bays over the past thirty years. In both areas the maximum size of fish, based on citation records, greatly increased from the late 1960\u27s until the mid-1980\u27s, as did the numbers of these large fish. These fluctuations appear to be due to a series of strong year classes, beginning in the late 1960\u27s

A Comparison Of A Validated Otolith Method To Age Weakfish, Cynoscion-Regalis, With The Traditional Scale Method

Otoliths, scales, dorsal spines, and pectoral-fin rays were compared to ascertain the best hardpart for determining the age of weakfish, Cynoscion regalis. Each showed concentric marks, which could be interpreted as annuli. Sectioned otoliths, however, consistently showed the clearest marks, had 100% agreement between and within readers, and were validated by the marginal increment method for ages 1-5. This validated method of ageing weakfish was then compared with the traditionally used scale method. The scale method was less precise, as demonstrated by lower percent agreement, and generally assigned younger ages for fish older than age 6 (as determined by otoliths). Consequently, mean sizes at age based on scales showed no clear signs of an asymptote, whereas those based on otoliths did. Otolith annuli formed in April and May, whereas scale annulus formation was more variable, ranging from April to August. This extended time of annulus formation made scales poorly suited for back calculation

Maturity, Spawning, And Ovarian Cycle Of Atlantic Croaker, Micropogonias-Undulatus, In The Chesapeake Bay And Adjacent Coastal Waters

The reproductive biology of Atlantic croaker, Micropogonias undulatus, collected during 1990-91 from commercial catches in Chesapeake Bay and in Virginia and North Carolina coastal waters (n=3,091), was studied by using macroscopic and microscopic gonad staging, the gonadosomatic index, oocyte diameter distributions, and histological analysis. Atlantic croaker are multiple spawners with asynchronous oocyte development and indeterminate fecundity. Mean length at first maturity for males and females was 182 and 173 mm TL, respectively. More than 85% of both sexes were mature by the end of their first year and all were mature by age 2. Spawning extends over a protracted period (July-December), but individual fish apparently spawn over a shorter interval. Eleven gravid and running-ripe females were collected within the Chesapeake Bay suggesting some spawning occurs in estuarine waters. Monthly sex ratios indicated a strong predominance of females during the main period of spawning. A high incidence of atretic, advanced yolked oocytes in spawning females collected throughout the spawning season suggests that a surplus production of yolked oocytes may be part of the reproductive strategy of Atlantic croaker

Development of Age Determination Methods, Life History/Population Dynamics Information, and Yield-per-Recruit Simulation Modeling to Evaluate the Potential for Growth and Recruitment Overfishing of Atlantic Croaker, Micropogonias undulatus, in the Chesapeake Bay

The Atlantic croaker, Micropogonias undulatus, supports large recreational fisheries in the Chesapeake Bay region, where it has historically shown large fluctuations in abundance. Although many studies have been conducted on this species in this region over the last 50 years or more, commencing at least as early as Wallace (1940), little or no information exists to support yield modeling and wise management. The present studies were undertaken to provide basic life history/population dynamics information and yield modeling needed to wisely manage this species in the Chesapeake Bay region, and to evaluate the role that fishing plays in their fluctuations. Accordingly, the basic objectives of the present studies were threefold: 1) To develop validated methods of age determination required to conduct basic life history/population dynamics studies, 2) To develop basic life history/population dynamics information required to conduct yield modeling, and 3) To conduct, as feasible, yield-per-recruit and eggsper- recruit modeling needed to evaluate growth overfishing, recruitment potential, and to provide advice for wise management

Yield-Per-Recruit Analysis And Management Strategies For Atlantic Croaker, Micropogonias Undulatus, In The Middle Atlantic Bight

The effect of different fishing mortality (F) and natural mortality (M), and age at first capture (t(c)) on yield-per-recruit of Atlantic croaker, Micropogonias undulatus, in the lower Chesapeake Bay and North Carolina were evaluated with the Beverton-Holt model. Independent of the level of M (0.20-0.35) or F (0.01-2.0) used in simulations, yield-per-recruit values for Chesapeake Bay were consistently higher at t(c) = 1 and decreased continuously with increases in t(c) (2-5). Although maximum yield per-recruit always occurred at the maximum level off (F=2.0), marginal increases in yield beyond F = 0.50-0.75 were negligible. Current F (F-CUR) is estimated to be below the level that produces maximum potential yield-per-recruit (F-MAX)and at or below the level of F-0.1 if M greater than or equal to 0.25. Although modeling results indicated yield-per-recruit could be maximized by reducing the current level of t(c) (t(c)=2), the resultant gains were small and did not appear to justify such management measures. Instead, it is suggested that regulatory measures be directed at maintaining the current level of t(c) in the lower Chesapeake Bay. Simulation results for North Carolina showed a pattern opposite to that shown for Chesapeake Bay, with yield-per-recruit curves increasing consistently with increases in t(c). Estimates of F-CUR for t(2) = 1 were consistently higher than F-0.1 as well as F-MAX, indicating that during the period 1979-81 Atlantic croaker were being growth-overfished in North Carolina. However, differences between Chesapeake Bay and North Carolina seem to reflect temporal rather than spatial differences in Atlantic croaker population dynamics, because data for North Carolina came from a period coinciding with the occurrence of unusually large Atlantic croaker along the east coast of the United States

Age, Growth, And Mortality Of Atlantic Croaker, Micropogonias-Undulatus, In The Chesapeake Bay-Region, With A Discussion Of Apparent Geographic Changes In Population-Dynamics

Atlantic croaker, Micropogonias undulatus, collected from commercial catches in Chesapeake Bay and in Virginia and North Carolina coastal waters during 1988-1991 (n=1,967) were aged from transverse otolith sections. Ages 1-8 were recorded, but eight-year-old fish were rare. Marginal increment analysis showed that for ages 1-7, annuli are formed once a year during the period April-May. Otolith age readings were precise: \u3e99% agreement within and between readers. Observed lengths-at-age were highly variable and growth rate decreased after the first year. Despite the high variability in sizes-at-age, observed lengths for ages 1-7 fit the von Bertalanffy growth model (r2=0.99; n=753) well. No differences in growth were found between sexes. Total annual instantaneous mortality (Z) estimated from maximum age and from a catch curve of Chesapeake Bay commercial catches ranged from 0.55 to 0.63. Our results do not indicate the existence of a group of larger, older Atlantic croaker in Chesapeake Bay compared with more southern waters and suggest that the hypothesis of a basically different population dynamics pattern for this species north and south of Cape Hatteras, North Carolina, should be reevaluated

Regional and Fishery-specific Patterns of Age and Growth of Yellowtail Snapper, Ocyurus chrysurus

We sampled yellowtail snapper, Ocyurus chrysurus, from commercial and recreational fisheries and fishery-independent surveys in the Atlantic Ocean off south Florida from 1980 through 2002. Specimens were collected primarily from two areas: Palm Beach and Monroe counties; collections were divided at 26° latitude into northern and southern populations. We collected sagittal otoliths and corresponding morphometric data from each population. Fork lengths (FL) ranged from 115 to 605 mm with a mean length of 312 mm. Yellowtail snapper were aged using sagittal otoliths with a high degree of precision [average percent error (APE) \u3c1%]. Ages ranged from 1 to 17 years, with mean ages of 3.96 years for the commercial fishery, 3.33 years for the recreational fishery, and 3.00 years for fishery-independent surveys. Yellowtail snapper entered the commercial and recreational fisheries by age 2; both fisheries were dominated by 2 and 3 year olds. The commercial fishery indicated the influence of a strong 1994 year class; this was not apparent in the recreational and fishery-independent surveys possibly due to small sample size. The von Bertalanffy growth curve parameters for all years and fishing modes combined [Lt = 410(1 - e-0.27(t+2.03))] were similar to previously published estimates for yellowtail snapper. The instantaneous total mortality rate of yellowtail snapper for all years and fishing modes combined (Z = 0.49) was also similar to previously published estimates. The total mortality rate for the northern population, Z = 0.67, was greater than for the southern population, Z = 0.45. Weight-length relationships were significantly different between northern and southern populations (P \u3c 0.001), and yellowtail snapper from the southern population were significantly larger and older than those from the northern population (P \u3c 0.001). Size-at-age was significantly larger for the most common ages (1--4 years) in the northern population compared to the southern population (age 1, P = 0.002; age 2--4, P \u3c 0.001 ). This may be due in part to differential fishing pressure; additional site-specific sampling is needed to elucidate the demographic differences between populations