Rodney D. Bertelsen

Fecundity dynamics of female spiny lobster (Panulirus argus) in a south Florida fishery and Dry Tortugas National Park lobster sanctuary

Using diver surveys, we compared the size structure, fecundity, and reproductive season of spiny lobsters (Panulirus argus) in the Dry Tortugas National Park lobster sanctuary with those of spiny lobsters in the south Florida fishery. The number of lobsters of both sexes larger than the legal size limit declined sharply in the fishery but not in the sanctuary. Clutch sizes were larger in the Dry Tortugas sanctuary, averaging 0.8 million, than in the fishery, averaging 0.3 million. The reproductive season was shorter and more intense in the sanctuary than in the fishery. In addition, lobsters in the sanctuary begin producing eggs at a larger size and produce more eggs per gram of body mass than lobsters in the fishery. Peak egg production occurs earlier in larger lobsters than in small ones. Establishing a fundamental reason for the differences between lobster reproduction in the sanctuary and that in the fishery is not possible until the chronological age of lobsters can be determined, but one hypothesis consistent with these differences is that, if lobsters reproduce at a certain chronological age, then sublethal fishery practices may account for slower growth for some lobsters resulting in some smaller but older reproductively active lobsters.

Neurolipofuscin Is a Measure of Age in Panulirus argus, the Caribbean Spiny Lobster, in Florida

Accurate age estimates for Panulirus argus, the commercially important Caribbean spiny lobster, would greatly enhance life history and population analyses. Most age approximations of P. argus are based on size and growth data, but size is generally considered a poor proxy for age of crustaceans in the field because of numerous environmental, density-dependent, and fishery-related factors. An established technique for aging crustaceans, employing histologically determined lipofuscin content in the nervous system, was investigated using known-age lobsters reared in the laboratory at ambient temperatures. We verified the presence of lipofuscin in eyestalk neural tissue by using autofluorescence and Sudan black staining and described its distribution in cell cluster A of the hemiellipsoid body. Neurolipofuscin accumulated with age; the overall trend was linear with indications of seasonal oscillation, whereas growth began to approach an asymptote after 3 years. Differences in the neurolipofuscin concentrations in the two eyestalks from the same animal were statistically insignificant. There was also no difference in the neurolipofuscin concentrations of males and females of the same age. The present data suggest a maximum potential lifespan for P. argus of about 20 years. These results also suggest that the neurolipofuscin technique will be valuable for estimating age of wild-caught specimens of P. argus.

Using acoustic tagging to determine adult spiny lobster (Panulirus argus) movement patterns in the Western Sambo Ecological Reserve (Florida, United States)

Abstract We used acoustic telemetry to study the movements of spiny lobster (Panulirus argus) during the spring and summer of 2003 and 2004 in Hawk Channel in the Western Sambo Ecological Reserve near Key West, Florida, United States. Overall, lobsters generally showed greatest movement after sunset and before sunrise with relatively less movement between midnight and 0200 h, however, there was great variability in movement patterns between individual lobsters and these variations were related to size or sex. Little or no movement occurred during daytime. Patterns of movement, as revealed by acoustic telemetry revealed that some lobsters repeatedly travelled to the same foraging area at the same time and then returned to the same patch reef (homing ability). Female lobsters that were reproductively active, exhibited movement patterns consistent with reproductive migrations to the forereef. These migrations lasted approximately 1 week and the lobster returned to the same patch reef presumably using the same homing ability used during daily activities. Although not statistically significant, the greatest overall daily total movement (total distance travelled) was found in small females. Small females also showed the greatest net daily movement (distance between denning locations) which suggests they had the highest rate of changing dens. The greater daily movement of small females did not convert to greater home ranges. There was no pattern in home range size with respect to the size and sex of lobsters.

Long‐term trends in the recreational lobster fishery of Florida, United States: Landings, effort, and implications for management

Abstract In Florida, United States, the Caribbean spiny lobster, Panulirus argus, supports an important commercial fishery and also perhaps the most intensive recreational fishery of any lobster species, with sales of recreational lobster fishing permits exceeding 100 000 annually. For the past decade, we have used mail surveys of recreational lobster license holders to estimate spatially explicit landings and fishing effort when recreational fishers are most active—during the states “Special Two‐Day Sport Season”, which takes place just before the opening of the commercial season, and during the first month of the regular recreational season, which coincides with the commercial season. From 1993 through 2002, fishing effort during the Special Two‐Day Sport Season has ranged from 60 000 to 112 000 person‐days, and landings have ranged from c. 112 to 255t. Both fishing effort and landings have varied without trend. Fishing effort during the regular season over the same period has ranged from 261 000 to 514 000 person‐days, and landings have ranged from 434 to 825 t. Fishing effort has shown a marginally statistically significant decreasing trend, the result of a progressive decrease in effort since 1999. The largest proportion of both fishing effort and landings was concentrated along the south‐east coast. Despite the recent decrease in landings, the proportion of total landings made by the recreational fishery has increased. From 1993 through 1998, the fishery was responsible for c. 30% of commercial landings; by 2001, that percentage increased to nearly 40%. Such a shift in landings away from the commercial trap fishery toward the recreational fishery was recognised as a potential but unintended effect of the ongoing management plan of restricting effort in the commercial trap fishery. Our 2001 surveys revealed that recreational lobster fishers spent more on a person‐day basis than the general visitor to the Florida Keys did, but less than those visitors using the regions coral reefs. Consequently, managers must establish management strategies that allow the coexistence of this resources user groups and also incorporate the social and environmental concerns of nonuser groups.

Using age to evaluate reproduction in Caribbean spiny lobster, Panulirus argus, in the Florida Keys and Dry Tortugas, United States

Abstract For many species of lobsters, size at sexual maturity varies across spatially separated populations. This is so for two populations of Caribbean spiny lobster, Panulirus argus, in southern Florida, where females from open‐fishing areas around the Dry Tortugas mature at a larger size than females from open‐fishing areas in the Florida Keys. Variations in onset of maturity between populations of lobsters have been attributed to different environmental conditions, lobster density, and/or fishing pressure. We used age as estimated by histologically expressed neurolipofuscin to examine differences in size at maturity in P. argus. Neurolipofuscin content measured in known‐age, laboratory‐reared animals in a previous study was used to estimate age in wild‐caught P. argus. We show that lobsters from the Florida Keys are significantly smaller than lobsters of the same age from the Dry Tortugas. This difference in growth rates between lobsters from the two locations likely explains the differences in size at onset of maturation. High rates of injury from fishery practices in the Florida Keys and differential predation on slow‐growing lobsters in the Dry Tortugas may account for these differences in growth rates. Additionally, we compared the ages of reproductive females collected from breeding grounds of the Florida Keys to same‐sized non‐reproductive females from an area in the Florida Keys where there was no evidence of breeding. We found that females possessing eggs early in the breeding season were significantly older than females that bore eggs later in the breeding season or that did not produce eggs. Older females also produced more clutches of eggs. Our research indicates that reproduction is related to age in P. argus. The intense fishery and the methods used to fish lobsters are the most likely causes of the reduction in spiny lobster population size structure and size at maturity.

Use of neurolipofuscin to determine age structure and growth rates of Caribbean spiny lobster Panulirus argus in Florida, United States

Abstract We histologically determined lipofuscin content in eyestalk neural tissue to estimate the age and growth of Caribbean spiny lobster (Panulirus argus) in Florida, United States. Neurolipofuscin was measured from size‐stratified samples of 145 lobsters from the Florida Keys and 119 lobsters from the Dry Tortugas, the two main fishing areas in Florida. Modal analysis of the neurolipofuscin concentration frequency histograms suggested a relatively constant neurolipofuscin accumulation rate of 0.27% by volume (%VF) per year, which corresponded with the annual accumulation rate of 0.29%VF previously measured in the laboratory. Verification of the similarity of neurolipofuscin accumulation rates for lobsters in the field with previous laboratory studies indicates that neurolipofuscin concentration is suitable for estimating population parameters for P. argus. Neurolipofuscin‐based age estimates of lobster populations from the Florida Keys and Dry Tortugas, developed from Monte Carlo simulations of size‐frequency distributions, suggested that legal‐sized lobsters (>76.2 mm carapace length) in both areas were predominately 1–2 years old. Lobsters from the Florida Keys were consistently smaller for their age than those from the Dry Tortugas, suggesting that their growth is slower and that there may be little movement of lobsters between the two areas.

Age determination method using neurolipofuscin: a reply to Buesa

Estimates of age of some types of animals such as fish and bivalves are possible by analysing hard structures such as otoliths, shells and vertebrae, which are retained throughout life and show agerelated changes. However, for animals such as crustaceans and other invertebrates that have no hard structures that persist throughout their lives, alternativemethods for determining age have emerged. One alternative method, and the one that we used in our 2009 paper in the New Zealand Journal of Marine and Freshwater Research (Matthews et al. 2009) and other work on the Caribbean spiny lobsterPanulirus argus (Maxwell et al. 2007, 2009, 2013), is histological quantification of lipofuscin in soft tissues. Lipofuscin is amixture of oxidised, cross-linked proteins that accumulate post-mitotically in cells of diverse types. They are associated with the lifespan of single post-mitotic cells, and thus also with the lifespan of the animal. Their rate of accumulation is correlated with metabolic activity, and thus they are an indicator of metabolic age more than chronological age. Lipofuscin has been used tomeasure the age inmany species, including humans, other vertebrates and also many invertebrates (e.g. Brunk & Terman 2002; Lomovasky et al. 2002; Porta 2002; Jung et al. 2007; Doubleday & Semmens 2011). Lipofuscin has been applied to the study of crustaceans. Beginning in the late 1980s, Matt Sheehy and colleagues pioneered using histologically measured neurolipofuscin for aging various species of crustaceans, including crayfish, clawed lobsters and spiny lobsters (Sheehy 1989, 1990a, 1992; Sheehy et al. 1996, 1998; de Kerros et al. 1995; Vila et al. 2000; Fonseca et al. 2003, 2005a,b). Other researchers have also used it for aging other crustacean species, including crayfish, American lobster, shrimp, ghost shrimp, amphipods and mantis shrimp (Wahle et al. 1996; Belchier et al. 1998; Bluhm&Brey 2001;Bluhm et al. 2001a,b;Kodama et al. 2006). In these studies, neurolipofuscin content has consistently been found to be more highly correlatedwith age than is size to age, becausewhile growth rates may vary with age, the free-radicalgenerating respiratory catabolism and lipofuscin accumulation continue. A central tenet of lipofuscin-age research is that lipofuscin accumulates predominately relative to chronological age and temperature, not somatic growth. In his critique of our work, Buesa concludes that ‘neurolipofuscin cannot be used to determine age structure and growth rates of the Caribbean spiny lobster Panulirus argus’. He bases this statement in large part on his assertion that the population of lobsters used to determine the ageneurolipofuscin content relationship in our study was not in the same physiological condition as our experimental animals. According to Buesa, our laboratory animals must have had a higher energy intake and lower energy expenditure than field animals, thus having a higher metabolic rate and different relationship between age and neurolipofuscin content compared to field animals. Buesa’s concerns that food availability may influence neurolipofuscin are not new and were directly