Timothy J. Pusack

Spatial and temporal patterns of larval dispersal in a coral-reef fish metapopulation: evidence of variable reproductive success

Many marine organisms can be transported hundreds of kilometres during their pelagic larval stage, yet little is known about spatial and temporal patterns of larval dispersal. Although traditional population‐genetic tools can be applied to infer movement of larvae on an evolutionary timescale, large effective population sizes and high rates of gene flow present serious challenges to documenting dispersal patterns over shorter, ecologically relevant, timescales. Here, we address these challenges by combining direct parentage analysis and indirect genetic analyses over a 4‐year period to document spatial and temporal patterns of larval dispersal in a common coral‐reef fish: the bicolour damselfish (Stegastes partitus). At four island locations surrounding Exuma Sound, Bahamas, including a long‐established marine reserve, we collected 3278 individuals and genotyped them at 10 microsatellite loci. Using Bayesian parentage analysis, we identified eight parent‐offspring pairs, thereby directly documenting dispersal distances ranging from 0 km (i.e., self‐recruitment) to 129 km (i.e., larval connectivity). Despite documenting substantial dispersal and gene flow between islands, we observed more self‐recruitment events than expected if the larvae were drawn from a common, well‐mixed pool (i.e., a completely open population). Additionally, we detected both spatial and temporal variation in signatures of sweepstakes and Wahlund effects. The high variance in reproductive success (i.e., ‘sweepstakes’) we observed may be influenced by seasonal mesoscale gyres present in the Exuma Sound, which play a prominent role in shaping local oceanographic patterns. This study documents the complex nature of larval dispersal in a coral‐reef fish, and highlights the importance of sampling multiple cohorts and coupling both direct and indirect genetic methods in order disentangle patterns of dispersal, gene flow and variable reproductive success.

Competitive interactions for shelter between invasive Pacific red lionfish and native Nassau grouper

The invasive Pacific red lionfish (Pterois volitans) poses a threat to western Atlantic and Caribbean coral reef systems. Lionfish are small-bodied predators that can reduce the abundance and diversity of native fishes via predation. Additionally, native predators or competitors appear to have a negligible effect on similarly sized lionfish. Nassau grouper (Epinephelus striatus) are a regionally endangered, large predator found throughout lionfish’s invasive range. Because lionfish and Nassau grouper occupy similar habitats and use similar resources, there is potential for competition between these two species. Using large, outdoor in-ground tanks, we investigated how lionfish and Nassau grouper affect each other’s behavior by comparing their distance from and use of shelter when in isolation versus when both species were in the presence of each other with limited shelter. We found that Nassau grouper, which displayed a high affinity for shelter in isolation, avoided lionfish in two distinct ways; (1) groupers positioned closer to and used limited shelter more when paired with similarly sized lionfish and (2) grouper moved much further away from shelter when paired with smaller lionfish. We also found that neither large lionfish nor large Nassau grouper preyed upon smaller individuals of the opposite species suggesting that Nassau grouper do not recognize small lionfish as prey. This study highlights how invasive lionfish may affect native Nassau grouper, and suggests that competition for shelter between these two species may be size dependent.

Threatened fishes of the world: Epinephelus itajara (Lichtenstein, 1822) (Epinephelidae, formerly Serranidae).

Common names: Goliath grouper, Jewfish, guasa, cherna. Conservation status: IUCN Red List — Critically Endangered A2d. Identification: Body is robust, elongate, brownish-yellow; black spots present on dorsum, cranium and fins becoming smaller with growth; small dorsal spines and rounded caudal fin. Head is broad and flat with relatively small eyes. Max size 250 cm, 320 kg (Heemstra and Randall 1993; Sadovy and Eklund 1999). Distribution: Recently found to occupy a smaller geographic range (Craig et al. 2008): the Gulf of Mexico, Caribbean, and tropical/subtropical waters of the Atlantic (Heemstra and Randall 1993). Abundance: Rare (Sadovy and Eklund 1999); number of spawning aggregations extirpated unknown; stocks in Florida and Eastern Gulf of Mexico recovering (Cass-Calay and Schmidt 2008). Habitat and ecology: Inhabits mangrove leaf detritus as larvae (Lara et al. 2009), estuaries and red mangroves as juveniles (Koenig et al. 2007), ledges, patch reefs, caves and wrecks as adults (Sadovy and Eklund 1999). Consumes crustaceans, fish, octopus, stingrays and juvenile hawksbill turtles and can live at least 37 years (Bullock et al 1992). Exhibits strong site fidelity (Sadovy and Eklund 1999). Reproduction: Mature at 4–6 years old at a size of 1100–1150 mm length (males) and 6–7 years 1200–1350 mm length (females), no evidence of protogynous hermaphroditism (Bullock et al. 1992). Nocturnal, aggregative spawning occurs from June-September-Caribbean (Bullock et al. 1992) and December-FebruaryBrazilian waters (Cavaleri-Gerhardinger et al. 2006) unresolved linkages to lunar phase (Mann et al 2008; Lara et al. 2009). Threats: Setlines, spearfishing, habitat destruction, (Sadovy and Eklund 1999; Graham et al. in press) and pollution (Evers et al. 2009). Conservation actions: Moratorium on fishing Environ Biol Fish (2009) 86:293–294 DOI 10.1007/s10641-009-9509-0

Can humans coexist with fishes

Deciding which textbook to assign to students is often a very difficult decision. A textbook should offer more than just a synthesis of information, it should inspire curiosity, cause one to reflect, and provide a framework for making decisions. Most reviews reflect a single opinion, sometimes based on personal preferences. What is missing from most reviews is an assessment of how a book affected students. We approach this book review differently. We present separate reviews by the instructors and the students participating in a graduate seminar on Fish Conservation. The class format was a mixture of guest lecturers and group discussion. Students were required to write critical comments about each chapter of the book. They understood that they would be co-authors on this review and critical assessment was necessary. The presumption is that similarities between two reviews suggest consensus, but that differences reflect honest differences of opinion as well as differences in background and experience.