Residency of bull sharks, Carcharhinus leucas (Carcharhiniformes: Carcharhinidae), at San Pedrillo Islet in Islas Murciélago, North Pacific of Costa Rica

Introduction: The bull shark, Carcharhinus leucas, is particularly vulnerable to anthropogenic actions because of its permanence in coastal ecosystems; populations depletion is registered in different places around the world. Aggregations of bull sharks have been reported in the North Pacific of Costa Rica, at Islas Murciélago, within the Guanacaste Conservation Area. Objective: To study the residency of bull sharks at San Pedrillo islet, Islas Murciélago. Methods: During the study period (June 2013 to February 2015) we used passive telemetry to tag 10 bull sharks. Results: All the sharks tagged were females, they were detected on 59 798 occasions by the acoustic receiver deployed in San Pedrillo. Acoustic signals from tagged sharks were received for a total period of 1 to 229 days (mean = 73.9 ± 71.3 days), with the last detections occurring on 9 January 2015. The Residency Index for each tagged shark across the entire monitoring period ranged from 0.41 to 1.00. The bull shark activity showed a significant pattern throughout the day at the receiver that specifically corresponded with the daily light cycle. Conclusions: This study concludes that San Pedrillo is an aggregation site (cleaning station) for bull sharks (C. leucas), possibly related to reproduction and not feeding behaviors.

Basking shark sub-surface behaviour revealed by animal-towed cameras

While biologging tags have answered a wealth of ecological questions, the drivers and consequences of movement and activity often remain difficult to ascertain, particularly marine vertebrates which are difficult to observe directly. Basking sharks, the second largest shark species in the world, aggregate in the summer in key foraging sites but despite advances in biologging technologies, little is known about their breeding ecology and sub-surface behaviour. Advances in camera technologies holds potential for filling in these knowledge gaps by providing environmental context and validating behaviours recorded with conventional telemetry. Six basking sharks were tagged at their feeding site in the Sea of Hebrides, Scotland, with towed cameras combined with time-depth recorders and satellite telemetry. Cameras recorded a cumulative 123 hours of video data over an average 64-hour deployment and confirmed the position of the sharks within the water column. Feeding events only occurred within a metre depth and made up ¾ of the time spent swimming near the surface. Sharks maintained similar tail beat frequencies regardless of whether feeding, swimming near the surface or the seabed, where they spent surprisingly up to 88% of daylight hours. This study reported the first complete breaching event and the first sub-surface putative courtship display, with nose-to-tail chasing, parallel swimming as well as the first observation of grouping behaviour near the seabed. Social groups of sharks are thought to be very short term and sporadic, and may play a role in finding breeding partners, particularly in solitary sharks which may use aggregations as an opportunity to breed. In situ observation of basking sharks at their seasonal aggregation site through animal borne cameras revealed unprecedented insight into the social and environmental context of basking shark behaviour which were previously limited to surface observations.

Marine Protected Areas (MPAs) as a Fisheries Management Tool for the Nassau Grouper (Epinephelus striatus) in Belize

The Nassau grouper, Epinephelus striatus, was once an important commercial fish species in the Caribbean, but is now considered commercially extinct throughout its range. Protection measures have included protection of adults via seasonal closures and spawning aggregation site reserves (SASRs). Marine protected areas (MPAs) are a promising fisheries management tool being used increasingly worldwide but are not specifically directed at the conservation of Nassau grouper. This thesis uses Belize as a case study location to determine how the established MPA network may contribute towards its protection. It was found that the Belize MPA network as a system may not contribute greatly, however, on an individual basis some MPAs contribute more to protection than others. Those MPAs which have characteristics most suitable for this species are Gladden Spit and Silk Cayes, Sapodilla Cayes, Bacalar Chico, Glovers Reef, Hol Chan, and South Water Caye Marine Reserves.

Marine Protected Areas (MPAs) as a Fisheries Management Tool for the Nassau Grouper (Epinephelus striatus) in Belize

The Nassau grouper, Epinephelus striatus, was once an important commercial fish species in the Caribbean, but is now considered commercially extinct throughout its range. Protection measures have included protection of adults via seasonal closures and spawning aggregation site reserves (SASRs). Marine protected areas (MPAs) are a promising fisheries management tool being used increasingly worldwide but are not specifically directed at the conservation of Nassau grouper. This thesis uses Belize as a case study location to determine how the established MPA network may contribute towards its protection. It was found that the Belize MPA network as a system may not contribute greatly, however, on an individual basis some MPAs contribute more to protection than others. Those MPAs which have characteristics most suitable for this species are Gladden Spit and Silk Cayes, Sapodilla Cayes, Bacalar Chico, Glovers Reef, Hol Chan, and South Water Caye Marine Reserves.

Fore reef location influences spawning success and egg predation in lek-like mating territories of the bird wrasse, Gomphosus varius

Many fish spawn in aggregations, but little is understood about the dynamics governing the success of spawning interactions. Here, we evaluate the influence that location of lek-like mating territories has on spawning interactions of Gomphosus varius. We used direct observations of spawning and egg predation events as well as local population counts to compare the rates of spawning, spawning interruptions, and predation on the eggs of G. varius at Finger Reef, Apra Harbor, Guam. We hypothesized that spawning rates would be highest among seaward locations that facilitate transport of pelagic larvae from reefs and that those territories would subsequently experience higher densities of egg predators, egg predation rates, and spawning interruptions. Male spawning success was highly skewed by mating territory location, with holders of the outer, seaward mating territories being more successful than those males holding territories in the middle and inner areas of the aggregation site. Within the outer territories, male mating success was also skewed by location. Egg predation was observed occasionally and increased linearly with bird wrasse spawning frequency. The population densities of egg predators were distributed equally across the study area. Spawning interruptions occurred most frequently within the inner zone of the spawning aggregation due to greater male-male aggression in intraspecific competition for females and territories. This study provides evidence that reef location influences the spawning success, egg predation rates, and spawning interruption rates of fishes that reproduce using lek-like mating territories.