Reproduction of blacknose shark (Carcharhinus acronotus) in coastal waters off northeastern Brazil

The blacknose shark, Carcharhinus acronotus, is a relatively small carcharinid, typically inhabiting continental shelf areas in the western Atlantic Ocean, from North Carolina throughout the Gulf of Mexico (Bigelow and Schroeder, 1948) and along the South American coast to Rio de Janeiro (Compagno, 1984). The abundance of this shark in nearshore areas throughout its distribution makes it accessible to commercial fishing, mainly from inshore hook-and-line and gill-net fisheries (Trent et al., 1997; Mattos and Hazin1)

Joint United States-Brazil Billfish Research in the Western South Atlantic

A joint research project between Brazilian and U.S. scientists was initiated in 2004 to investigate the interaction of istiophorid billfishes with pelagic longline fisheries in the western equatorial South Atlantic Ocean. This project incorporates two general themes (1) an investigation into several aspects of pelagic longline operations by comparing catch results between circle and “J” style hooks, time-of-capture with hook time recorders, and by direct monitoring of pelagic longline gear behavior, and (2) an additional evaluation of billfish trophic ecology using a combination of satellite tag technology and traditional analyses (e.g., gut contents and ageing). Data obtained from this research will provide additional data for the evaluation of habitat-based stock assessment modeling efforts for billfish and other pelagic fish species

Fishing Gear Modifications to Reduce Elasmobranch Mortality in Pelagic and Bottom Longline Fisheries Off Northeast Brazil

One of the biggest challenges of fisheries research is reducing the bycatch of unwanted species. The incidental fishing mortality of species with low reproductive rates, such as elasmobranchs (sharks, skates, and rays), is recognized as a key threat for their populations. In the present study, gear modifications related to the type of hook and position of the hook in the water column were tested to examine their effects on catch rates and mortality of elasmobranch species in both pelagic and coastal environments. Comparisons between circle (size 18/0, 0° offset) and J-style (size 9/0, 10° offset) hooks demonstrated that the circle hooks have a greater efficiency in reducing the mortality of most species caught, both in pelagic and coastal longline fisheries. Internal lodging of the hook was significantly less frequent for the individuals caught with circle hooks, which likely contributed to their higher survival rate at haulback. Additionally, circle hooks also increased the CPUE of elasmobranchs caught in the pelagic longline fishery, which was particularly evident for Carcharhinus falciformis and Prionace glauca. The position of the hook in the water column exhibited a strong influence on the species caught in the coastal bottom longline fishery. Suspending hooks in the middle of the water column reduced the bycatch of common demersal species, such as Carcharhinus acronotus, Ginglymostoma cirratum, and Dasyatis americana, while increasing the CPUE of potentially aggressive species, such as Galeocerdo cuvier and Carcharhinus leucas. The interaction of the type of hook utilized with its position in the water column appears to be an essential factor in the optimization of longline selectivity and minimization of bycatch mortality

Preliminary Results of Circle and J-Style Hook Comparisons in the Brazilian Pelagic Longline Fishery

Preliminary studies in western North Atlantic pelagic longline fisheries indicate that a change in terminal gear from J-style hooks to circle hooks may reduce bycatch mortality. However, such studies have not examined the impact of this change in the equatorial fishery. Catch composition, catch rates, hooking location, and condition at haulback were monitored during 26 sets in the commercial longline fishery operating in the western equatorial South Atlantic where circle (size 18/0, non-offset) and J-style (size 9/0 and 10/0, 10° offset) hooks were deployed in an alternating fashion. Catch rates for yellowfin tuna, swordfish, and a composite “all fishes” category were significantly (P \u3c 0.05) higher for circle hooks. Bigeye tuna, swordfish, sailfish, and yellowfin tuna were hooked significantly more often externally than internally. Yellowfin tuna were over eight times more likely to be hooked in the mouth with circle hooks than with J-style hooks. Bigeye tuna and sailfish showed significantly higher rates of survival at haulback with circle hooks. The results suggest that the use of size 18/0 non-offset circle hooks in the equatorial pelagic longline fishery may increase the survival of bycatch species at haulback with minimal detrimental effects on the catches of target species

Comparative Population Genetics and Evolutionary History of Two Commonly Misidentified Billfishes of Management and Conservation Concern

Background: Misidentifications between exploited species may lead to inaccuracies in population assessments, with potentially irreversible conservation ramifications if overexploitation of either species is occurring. A notable showcase is provided by the realization that the roundscale spearfish (Tetrapturus georgii), a recently validated species, has been historically misidentified as the morphologically very similar and severely overfished white marlin (Kajikia albida) (IUCN listing: Vulnerable). In effect, no information exists on the population status and evolutionary history of the enigmatic roundscale spearfish, a large, highly vagile and broadly distributed pelagic species. We provide the first population genetic evaluation of the roundscale spearfish, utilizing nuclear microsatellite and mitochondrial DNA sequence markers. Furthermore, we re-evaluated existing white marlin mitochondrial genetic data and present our findings in a comparative context to the roundscale spearfish. Results: Microsatellite and mitochondrial (control region) DNA markers provided mixed evidence for roundscale spearfish population differentiation between the western north and south Atlantic regions, depending on marker-statistical analysis combination used. Mitochondrial DNA analyses provided strong signals of historical population growth for both white marlin and roundscale spearfish, but higher genetic diversity and effective female population size (1.5-1.9X) for white marlin. Conclusions: The equivocal indications of roundscale spearfish population structure, combined with a smaller effective female population size compared to the white marlin, already a species of concern, suggests that a species-specific and precautionary management strategy recognizing two management units is prudent for this newly validated billfish

Beyond Post-release Mortality: Inferences on Recovery Periods and Natural Mortality From Electronic Tagging Data for Discarded Lamnid Sharks

Accurately characterizing the biology of a pelagic shark species is critical when assessing its status and resilience to fishing pressure. Natural mortality (M) is well known to be a key parameter determining productivity and resilience, but also one for which estimates are most uncertain. While M can be inferred from life history, validated direct estimates are extremely rare for sharks. Porbeagle (Lamna nasus) and shortfin mako (Isurus oxyrinchus) are presently overfished in the North Atlantic, but there are no directed fisheries and successful live release of bycatch is believed to have increased. Understanding M, post-release mortality (PRM), and variables that affect mortality are necessary for management and effective bycatch mitigation. From 177 deployments of archival satellite tags, we inferred mortality events, characterized physiological recovery periods following release, and applied survival mixture models to assess M and PRM. We also evaluated covariate effects on the duration of any recovery period and PRM to inform mitigation. Although large sample sizes involving extended monitoring periods (>90 days) would be optimal to directly estimate M from survival data, it was possible to constrain estimates and infer probable values for both species. Furthermore, the consistency of M estimates with values derived from longevity information suggests that age determination is relatively accurate for these species. Regarding bycatch mitigation, our analyses suggest that juvenile porbeagle are more susceptible to harm during capture and handling, that keeping lamnid sharks in the water during release is optimal, and that circle hooks are associated with longer recovery periods for shortfin mako.En prens

Reproductive biology of dolphinfish, <em>Coryphaena hippurus</em> (Actinopterygii: Coryphaenidae), in Saint Peter and Saint Paul Archipelago, Brazil

In order to elucidate the main aspects related to dolphinfish reproduction around Saint Peter and Saint Paul Archipelago, 862 individuals caught in that area by commercial handline fishing were examined between 2007 and 2011. From those specimens, it was possible to assess the sex in 782 specimens (271 males and 511 females) and the levels of gonadal maturation in 536 of them (175 males and 361 females). The fork length (FL) of the examined specimens varied between 27 and 150 cm. Sex ratio found was 1.0 male: 1.9 females, but the difference was not statistically significant in April (χ2=0.08), August (χ2=0.82) and October (χ2=3.63). However, by size interval, sex ratio was 1.0 male: 1.0 female for FL between 120 and 130 cm. The gonadal index showed the highest values in February for males and in April for females. Most spawning-capable specimens were found in February (males 36.4%) and in May (females 42.2%). The length of size-at-50%-maturity (L50) was estimated at 70.66 cm FL for males and 68.60 cm FL for females. The results suggest that the period of highest reproductive activity occurs between April and June

Biología reproductiva del dorado, Coryphaena hippurus (Actinopterygii: Coryphaenidae), en el Archipiélago de San Pedro y San Pablo, Brasil

In order to elucidate the main aspects related to dolphinfish reproduction around Saint Peter and Saint Paul Archipelago, 862 individuals caught in that area by commercial handline fishing were examined between 2007 and 2011. From those specimens, it was possible to assess the sex in 782 specimens (271 males and 511 females) and the levels of gonadal maturation in 536 of them (175 males and 361 females). The fork length (FL) of the examined specimens varied between 27 and 150 cm. Sex ratio found was 1.0 male: 1.9 females, but the difference was not statistically significant in April (χ2=0.08), August (χ2=0.82) and October (χ2=3.63). However, by size interval, sex ratio was 1.0 male: 1.0 female for FL between 120 and 130 cm. The gonadal index showed the highest values in February for males and in April for females. Most spawning-capable specimens were found in February (males 36.4%) and in May (females 42.2%). The length of size-at-50%-maturity (L50) was estimated at 70.66 cm FL for males and 68.60 cm FL for females. The results suggest that the period of highest reproductive activity occurs between April and June.Con el objetivo de estudiar la reproducción del dorado capturado con línea de mano por la flota pesquera en los alrededores del Archipiélago de San Pedro y San Pablo, entre 2007 y 2011 se examinaron un total de 862 ejemplares de esta especie. Fue posible identificar el sexo de 782 de estos ejemplares (271 machos y 511 hembras), así como los estados de madurez gonadal de 536. La longitud furcal (LF) de los ejemplares examinados varió entre 27 y 150 cm. La proporción de sexos fue de 1 macho por 1.9 hembras, aunque en abril (χ2=0.08), agosto (χ2=0.82) y octubre (χ2=3.63) la proporción de sexos no fue significativamente diferente de 1:1, ni en los ejemplares entre 120 y 130 cm LF. El índice gonadal mostró mayores valores en febrero para machos y en abril para hembras. El mayor porcentaje de individuos maduros se observó en febrero y mayo. La talla de primera madurez sexual (L50) se estimó en 70.66 cm LF para machos y 68.60 cm LF para hembras. Los resultados sugieren que el periodo de mayor intensidad reproductiva se sitúa entre abril y junio

Broad Geographic Distribution of Roundscale Spearfish (Tetrapturus georgii) (Teleostei, Istiophoridae) in the Atlantic Revealed by DNA Analysis: Implications for White Marlin and Roundscale Spearfish Management

The recent validation of the roundscale spearfish (Tetrapturus georgii) within the western North Atlantic has introduced new complexities in the management of the overfished white marlin (Kajikia albida) in this region due to historical and contemporary misidentification between the two morphologically similar species. Compounding the management challenge for white marlin, which is currently assessed as a single Atlantic-wide stock, is an unclear picture of the extent of the roundscale spearfish\u27s overall Atlantic distribution. By using genetic tools (mitochondrial DNA ND4L-ND4 locus sequences) for species identification, we confirm that the roundscale spearfish has a much broader distribution than previously known, including the central North Atlantic and much of the western South Atlantic to at least 28°52′S. This much wider Atlantic distribution of the roundscale spearfish sympatric with its morphologically similar congeners, the white marlin and longbill spearfish (Tetrapturus pfluegeri), raises further management complexities: it increases the geographic scale for species misidentification in catch records that form the basis for stock assessments and uncertainty in currently accepted white marlin biological parameters. Additional vigilance in obtaining accurate species identification by improved fishery onboard observer training and incorporation of genetic tools is recommended for informing management of white marlin, longbill spearfish and roundscale spearfish throughout the Atlantic