Thomas R. Matthews

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.

Lobster trap impact on coral reefs: Effects of wind‐driven trap movement

Abstract Commercial fishers report finding their lobster traps often great distances from their original location following major hurricanes. But traps also move during lesser wind events, such as during winter cold fronts. To assess trap impact on coral communities following winter storms, lobster traps were placed in hardbottom and reef habitats commonly used by commercial fishers in the Florida Keys, United States. Trap movement, percentage benthic faunal cover, and benthic faunal damage were assessed after 26 wind events occuring over three winters. Traps moved when storms with sustained winds greater than 15 knots (27.8 km/h) persisted for more than 2 days. Winter storms above this threshold moved buoyed traps a mean (±SE) distance of 3.63 ± 0.62 m, 3.21 ± 0.36 m, and 0.73 ± 0.15 m per trap and affected a mean area of 4.66 ± 0.76 m2, 2.88 ± 0.29 m2, and 1.06 ± 0.17 m2, per trap at 4‐m, 8‐m, and 12‐m depths, respectively. Unbuoyed traps, simulating derelict traps, moved a mean distance of 0.43 ± 0.08 m and 0.44 ± 0.02 m, and affected a mean area of 0.77 ± 0.06 m2 and 0.90 ± 0.08 m2 per trap at 4‐m and 8‐m depths, respectively. Injuries caused by trap movement included scraped, fragmented, and dislodged sessile fauna, resulting in significant damage to stony coral, octocoral, and sponges. Overall, sessile fauna cover along the trap movement path was reduced from 45% to 31%, 51% to 41%, and 41% to 35% at the 4‐m, 8‐m, and 12‐m sites, respectively. Because of the large numbers of traps deployed and reported lost each season, damage to sessile fauna and loss of benthic faunal cover caused by traps needs to be considered to effectively protect coral reefs and manage essential fishery habitat in the future.

Trap-induced mortality of the spiny lobster, Panulirus argus, in Florida, USA

In Florida’s lobster fishery, sublegal-sized spiny lobsters, Panulirus argus, are commonly placed in traps to attract legal-sized lobsters. Many died from exposure to air during transport before the use of live wells and still die because of confinement in traps. Much of this mortality is not apparent during normal trap-fishing operations, and the magnitude of the unobserved mortality remains the subject of controversy between fishermen and fishery managers. After fishermen began using live wells in the 1987–88 fishing season, the harvest of legalsized lobsters increased. Initially, the increase was smaller than predicted, apparently because the average number of traps in the fishery increased from 576 000 during the 1977–78 to 1986–87 fishing seasons to 854 000 during the 1987–88 to 1992–93 seasons. High numbers of traps in the fishery have been implicated as contributing to increased mortality of sublegal-sized lobsters. When the average number of traps was reduced to 605 000, after the 1993–94 season, the harvest predictions attributed to live-well use were largely achieved. Observations on commercial fishing vessels were used to reevaluate previous harvest predictions and develop additional coefficients for fishing mortality related to exposure and confinement in traps.

Distribution, Prevalence, and Genetic Analysis of Panulirus Argus Virus 1 (Pav1) from the Caribbean Sea

The pathogenic virus Panulirus argus virus 1 (PaV1) was first discovered in Caribbean spiny lobsters Panulirus argus from the Florida Keys (USA) in 1999 and has since been reported in Belize, Mexico, and Cuba; its distribution in the wider Caribbean is unknown. We collected tissue samples from adult spiny lobsters from 30 locations in 14 countries bordering the Caribbean Sea and used molecular diagnostics to assay for the presence of PaV1. PaV1 occurred primarily in the northern areas of the Caribbean, where its prevalence was highest. The virus was not found in lobsters from the southeastern Caribbean, and its prevalence was lowest in the southwestern Caribbean. DNA sequence analysis was performed on a fragment of the viral DNA to examine the genetic diversity of PaV1 on a Caribbean-wide scale. Sequence variation in the viral DNA fragment was high, with 61 unique alleles identified from 9 areas. The sharing of viral alleles in lobsters from distant locations supports the hypothesis of a strong genetic connectivity among lobsters within the Caribbean, and further supports the hypothesis that postlarvae infected with PaV1 may serve to disperse the virus over long distances.

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.

Lobster Trap Debris in the Florida Keys National Marine Sanctuary: Distribution, Abundance, Density, and Patterns of Accumulation

AbstractThe fishery for spiny lobster Panulirus argus in the Florida Keys National Marine Sanctuary is well chronicled, but little information is available on the prevalence of lost or abandoned lobster traps. In 2007, towed-diver surveys were used to identify and count pieces of trap debris and any other marine debris encountered. Trap debris density (debris incidences/ha) in historic trap-use zones and in representative benthic habitats was estimated. Trap debris was not proportionally distributed with fishing effort. Coral habitats had the greatest density of trap debris despite trap fishers’ reported avoidance of coral reefs while fishing. The accumulation of trap debris on coral emphasizes the role of wind in redistributing traps and trap debris in the sanctuary. We estimated that 85,548±23,387 (mean±SD) ghost traps and 1,056,127±124,919 nonfishing traps or remnants of traps were present in the study area. Given the large numbers of traps in the fishery and the lack of effective measures for managing...

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