Discussion

Age and Growth Rates

         Small prey species are often presumed to be relatively short-lived. A perhaps surprising and significant finding from the present study is that the small serranids dominant on NEGOM reefs were older than their typical inshore forage-fish counterparts. The oldest specimens of P. martinicensis, H. vivanus, and S. phoebe examined were age-IX, age-VIII, and age-V, respectively.  Many comparative small prey species from inshore waters, such as ballyhoo (Hemiramphus brasiliensis), bay anchovy (Anchoa mitchilli), and scaled sardine (Harengula jaguana), rarely live beyond one year (Lapolla 2001, McBride and Thurman 2003, Pierce et al. 2001). Other, much larger serranid species such as scamp (Mycteroperca phenax), gag (Mycteroperca microlepis), and red grouper (Epinephelus morio) are relatively long-lived, with maximum observed ages of 30, 21, and 48 years, respectively (Harris et al. 2002, Hood and Schlieder 1992, Johnson and Collins 1994). Age estimates from otoliths of other small serranid species have yielded results similar to ours.  Black seabass (Centropristis striata) and sand perch (Diplectrum formosum) attain maximum ages of seven and six, respectively (Bortone 1971, Hood et al. 1994).  Known maximum ages of other reef families (Lutjanidae, Labridae and Pomacentridae) exceed seven years (Burton 2001, Dulcic and Draljevic 1995, Fowler and Doherty 1992, Hood 1999, McBride 2001).  Thus, our age estimates for the three serranid species analyzed in the present study are consistent with those for other small reef-fish species.

         The spatial variations observed in P. martinicensis growth rates for different reef populations deserve further inquiry. Similar variations have also been observed in other serranid species. Populations of C. striata off the southeastern United States exhibited latitudinal variations in size-at-age (McGovern et al. 2002).  Regional variations have also been observed in the size at sexual transition in another protogynous anthiine, Anthias squamipinnis (Fishelson 1975, Popper and Fishelson 1973, Shapiro 1979).   In these studies the minimum size at transition for A. squamipinnis ranged from 65-100 mm total length.  Low sample sizes of female and transitional P. martinicensis prevented spatial comparisons of reproductive data.

         The factors responsible for spatial variations in P. martinicensis growth rates are unknown. However, there are most likely a number of factors influencing this trend.   In other aquatic ecosystems, predation, food availability, and quality of the environment have been shown to influence the size structure of fish populations (Paukert et al. 2002). Unfortunately, sufficient coordinated physical and biological habitat parameter data do not exist to determine what factors influence P. martinicensis demo-graphics.

         An alternative explanation of differential modal fish size for different NEGOM reefs may be the effects of varying anthropogenic impacts from fishing pressure.  All NEGOM reefs have been exploited for decades by both the commercial and recreational fisheries. Differential rates of removal of large piscivores may result in differences in abundance, modal size, and behavior of small serranid planktivores.

       Whole otoliths proved preferable for use in aging the serranid samples available in the present study. The relatively small size of otoliths examined permitted sufficient reflected light to penetrate the otolith and allowed the denser annuli to be viewed.  In sectioned serranid otoliths, the annuli tend to split into two or more rings, which could lead to an over-estimation of age. In whole otoliths, these small imperfections are blended together making the annuli more visible. Most other serranid age estimates available in the literature have been derived from sectioned otoliths. However, previous serranid aging studies have dealt mostly with large species from the commercial fishery (e.g., E. morio, M. phenax, M. microlepis, and C. striata) (Harris et al. 2002, Hood and Schlieder 1992, Hood et al. 1994, Johnson and Collins 1994). The much larger otoliths in these species have generally required otolith sectioning in order to count annual rings. Whole sagittal otoliths have been used to age another small serranid, D. formosum, in Florida waters (Bortone 1971). Scales have been shown to be less reliable than otoliths because they underestimate ages of fish older than age-VI (Lowerre-Barbieri et al. 1994).

         In contrast to the relative ease of identifying annuli on serranid otoliths, C. enchrysurus otoliths were considered difficult to age.  While concentric rings were visible, they were more difficult to distinguish from one another.  Moreover, the limited sample size and lack of C. enchrysurus specimens from throughout the year prevented otolith validation in our study.  Nonetheless, our age estimates (maximum age=XI) correspond closely with validated ages of other pomacentrids. For example, maximum validated ages for Pomacentrus moluccensis and P. wardi have been reported as age-IX and age-X, respectively (Fowler and Doherty 1992). Specimens of C. enchrysurus of different ages also displayed little variation in SL (Figure 26). Presumably this is a result of sampling bias from hook and line sampling. As was evident for the other species aged, young C. enchrysurus (age-0, age-I, and age-II) are under-represented in our samples.  In order to complete an accurate length versus weight regression and validate C. enchrysurus otoliths more sampling of this species is needed.

         The longevity exhibited by P. martinicensis, H. vivanus, S. phoebe, and C. enchrysurus enables an estimate of post-disturbance recovery time for dominant prey fish species and the overall deep-reef ecosystem. For example, if a natural disaster (i.e., hurricane or red tide) or human impact suddenly removed all species from a deep OCS reef, it would take a minimum of nine years for P. martinicensis populations to return their previous demographics. This assumes that habitat quality was not fundamentally impaired by the disturbance. However, in the case of an oil spill, recovery may take longer.  For example, following an oil spill in a temperate coastal bay, oil residues were still present after six years, and contamination still evident in fish tissue after eight years (Keizer et al. 1978, Stegeman 1978).

Reproduction

         Pronotogrammus martinicensis and H. vivanus are both protogynous hermaphrodites, as are many other anthiine serranids such as Anthias squamipinnis, and Hemanthias peruanus (Coleman 1983, Fishelson 1975, Popper and Fishelson 1973, Shapiro 1979).  Although previous research had described both species as protogynous (Coleman 1981, Hastings 1981), our study describes the reproductive biology of both species in more detail, and presents one contrary finding.  Coleman (1981) described a single P. martinicensis as having a gonad with spermatogenesis and oogenesis occurring simultaneously, but in our large sample, we found no evidence of simultaneous hermaphrodism in this species.

         Our determinations of the mean SL of transitional P. martinicensis and H. vivanus corresponded closely with the lengths at transitions previously reported. Coleman (1981) described transitional P. martinicensis as ranging from 73-94 mm SL (mean = 81.6 mm). In our study, transitional P. martinicensis from the NEGOM ranged from 71-104 mm SL (mean SL = 85 mm).  The mean SL of H. vivanus in the NEGOM has not changed in the past 20 years.  Hastings (1981) observed transitional specimens ranging from 65-74 mm SL (mean SL = 68.6). Transitional H. vivanus collected in our study ranged in SL from 49-77 mm (mean SL = 67 mm).

         Our limited fecundity data suggests that body size and weight are not useful indicators of batch fecundity for P. martinicensis.  Further sampling is required to verify this lack of a trend.  The hydrated females collected indicated a potentially narrow size range among spawning females.  Together with a limited number of data points, this makes it difficult to model a statistically significant regression.  We did not determine batch fecundity estimates for H. vivanus or S. phoebe.  During this study, no hydrated H. vivanus were collected, presumably the result of the small size of H. vivanus females (< 77 mm SL). Serranus phoebe gonads are un-delimited and the male tissue is located on the anterior periphery of the gonad. As a result, female and male tissue cannot be easily separated in order to make accurate oocyte counts.

         Serranus phoebe is a simultaneous hermaphrodite.  We found no indications of alternative reproductive modes.  Serranus baldwini and S. fasciatus populations have been described to contain both simultaneous hermaphrodites and larger terminal males (Hastings and Petersen 1986, Petersen and Fischer 1986, Petersen 1987).  In contrast, we found no indication of a terminal male stage in S. phoebe populations in the NEGOM.  Although all histological samples examined contained ovarian tissue, testicular material was not visible in all histological samples. Nonetheless, S. phoebe populations do not appear to contain a solely female reproductive stage.  The testicular tissue is located on the anterior section of the gonad and was visible macroscopically in all gonads.  During histological processing, male tissue was occasionally, but inadvertently omitted.  This depended on the size of the gonad and which side of the transverse section was used for histological slide preparation.

         The more detailed knowledge of species life histories developed during the present study provides a better understanding of outer-continental shelf reef ecology.  This knowledge also provides insights that may prove useful in fisheries management and conservation.  As a result of fishing pressure, many deep-reef ecosystems have experienced temporal changes in the relative abundance of the benthic predators that probably control community structure to a large extent. Benthic predators (e.g., M. phenax, M. microlepis, C. striata, and Epinephelus niveatus) declined in relative abundance from 50% to 5% of total observed fish species on Jeff's Reef from 1980-1995, while prey species (P. martinicensis and H. vivanus) increased in relative abundance from 6% to 71% (Koenig et al. 2000). In recent years, declines in economically-important benthic predators have resulted in a variety of management regulations, ranging from increased size of minimum harvest to the establishment of marine protected areas. By further understanding the interactions between predator and prey species, researchers are better able to predict the causes and effects of these changes in species abundance, thereby facilitating more effective management of marine ecosystems.