Tiger Grouper ( Mycteroperca tigris ) form fish spawning aggregations (FSAs) around the winter full moons (typically January through April) in the Caribbean. Males defend territories to attract mates in a lek-like reproductive strategy. Prior studies have documented rapid declines in populations with FSA-associated fisheries. This study examines the migratory behavior of adult male Tiger Grouper in Little Cayman, Cayman Islands, to better understand the impacts of aggregation fishing. As part of the Grouper Moon Project, we acoustically tagged ten spawning male Tiger Grouper at the western end of Little Cayman in February 2015. Using a hydrophone array surrounding the island, we tracked the movements of the tagged fish for 13 months. We observed 3 migratory strategies: resident fish ( n = 2) that live at the FSA site, neighboring fish ( n = 5) that live within 4 km of the site, and commuter fish ( n = 3) that travel over 4 km for spawning. Fish began aggregating 2 days before the full moon and left 10–12 days after the full moon, from January to May. Regardless of migratory strategy, all tagged fish that aggregated after February 2015 returned to the west end FSA. However, in January 2016, one fish appeared to attend a different FSA closer to its presumed home territory. Tiger Grouper may establish multiple FSAs around Little Cayman, and males appear to attend FSAs near their home territories. Protracted spawning seasons, FSA site infidelity, and putative FSA catchments should all be considered to ensure sustainable fisheries management for this important species.

Dispersal of eggs and larvae from spawning sites is critical to the population dynamics and conservation of marine fishes. For overfished species like critically endangered Nassau grouper ( Epinephelus striatus ), recovery depends on the fate of eggs spawned at the few remaining aggregation sites. Biophysical models can predict larval dispersal, yet these rely on assumed values of key parameters, such as diffusion and mortality rates, which have historically been difficult or impossible to estimate. We used in situ imaging to record three-dimensional positions of individual eggs and larvae in proximity to oceanographic drifters released into egg plumes from the largest known Nassau grouper spawning aggregation. We then estimated a diffusion–mortality model and applied it to previous years' drifter tracks to evaluate the possibility of retention versus export to nearby sites within 5 days of spawning. Results indicate that larvae were retained locally in 2011 and 2017, with 2011 recruitment being a substantial driver of population recovery on Little Cayman. Export to a nearby island with a depleted population occurred in 2016. After two decades of protection, the population appears to be self-replenishing but also capable of seeding recruitment in the region, supporting calls to incorporate spawning aggregation protections into fisheries management.

Understanding how reef-associated sharks use coastal waters through their ontogeny is important for their effective conservation and management. This study used the horizontal movements of acoustically tagged Caribbean reef sharks ( Carcharhinus perezi ) to examine their use of coastal space around the Cayman Islands between 2009 and 2019. A total of 39 (59.1%) tagged sharks (male = 22, female = 17, immature = 18, mature = 21) were detected on the islands wide network of acoustic receivers. The detection data were used to calculate values of Residency Index (RI), Site-Fidelity Index (SFI) and minimum linear displacement (MLD), as well as for network analysis of individual shark movements to test for differences between demographics, seasons, and diel periods. Sharks were detected for up to 1,598 days post-tagging and some individuals showed resident behaviour but the majority of tagged individuals appear to have been one-off or only occasional transient visitors to the area. Generally, individuals showed strong site-fidelity to different areas displaying linear home ranges of < 20 km. The evidence indicates that there was no pattern of diel behaviour. Tagged sharks generally showed increased movements within and between islands during the summer (April–September), which may be related to breeding activity. Some individuals even made occasional excursions across 110 km of open water > 2,000 m deep between Grand Cayman and Little Cayman. One mature female shark showed a displacement of 148.21 km, the greatest distance reported for this species. The data shows that the distances over which some sharks moved, greatly exceeded the extent of any one of the islands’ marine protected areas indicating that this species may be more mobile and dispersive than previously thought. This study provides support for the blanket protection to all sharks throughout Cayman waters, which was incorporated within the National Conservation Act in 2015.

Characterizing the behavior of coral reef fishes at home reef sites can provide insight into the mechanisms of spatial ecology and provide a framework for spatial resource management. In the Caribbean, populations of Nassau grouper Epinephelus striatus have declined due to fishing impacts on spawning aggregations. Despite local and regional efforts by fisheries managers to implement regulations protecting spawning aggregations, few Nassau grouper populations appear to be recovering. In order to improve management strategies for this critically endangered species, it is necessary to understand the spatial ecology of the species across seasons and years. In the Cayman Islands, we used a multi-year, presence/absence, depth-coded acoustic tagging dataset of Nassau grouper to characterize patterns in the species’ behavior and vertical habitat use at home reef sites. Twenty acoustically tagged individuals (56-84 cm, 70.01 ± 7.40 cm; total length, mean ± SD) maintained consistent home reef sites, although some fish regularly shifted activity centers within the home site, often following a seasonal spawning migration. Seven fish with depth-coded tags showed a higher probability of vertical movement in the hours immediately following dawn and preceding dusk. We found evidence of a positive relationship between the fish condition factor and depth of home reef site. The finding of persistent home reef sites across years suggests that properly sized spatial reserves at home reef sites can be a useful complement to spawning aggregation protection when considering management strategies for Nassau grouper.

Many large-bodied marine fishes that form spawning aggregations, such as the Nassau grouper (Epinephelus striatus), have suffered regional overfishing due to exploitation during spawning. In response, marine resource managers in many locations have established marine protected areas or seasonal closures to recover these overfished stocks. The challenge in assessing management effectiveness lies largely in the development of accurate estimates to track stock size through time. For the past 15 y, the Cayman Islands government has taken a series of management actions aimed at recovering collapsed stocks of Nassau grouper. Importantly, the government also partnered with academic and nonprofit organizations to establish a research and monitoring program (Grouper Moon) aimed at documenting the impacts of conservation action. Here, we develop an integrated population model of 2 Cayman Nassau grouper stocks based on both diver-collected mark-resight observations and video censuses. Using both data types across multiple years, we fit parameters for a state-space model for population growth. We show that over the last 15 y the Nassau grouper population on Little Cayman has more than tripled in response to conservation efforts. Census data from Cayman Brac, while more sparse, show a similar pattern. These findings demonstrate that spatial and seasonal closures aimed at rebuilding aggregation-based fisheries can foster conservation success.

Biogeochemical hot moments occur when a temporary increase in availability of one or more limiting reactants results in elevated rates of biogeochemical reactions. Many marine fish form transient spawning aggregations, temporarily increasing their local abundance and thus nutrients supplied via excretion at the aggregation site. In this way, nutrients released by aggregating fish could create a biogeochemical hot moment. Using a combination of empirical and modeling approaches, we estimate nitrogen and phosphorus supplied by aggregating Nassau grouper (Epinephelus striatus). Data suggest aggregating grouper supply up to an order-of-magnitude more nitrogen and phosphorus than daily consumer-derived nutrient supply on coral reefs without aggregating fish. Comparing current and historic aggregation-level excretion estimates shows that overfishing reduced nutrients supplied by aggregating fish by up to 87 %. Our study illustrates a previously unrecognized ecosystem viewpoint regarding fish spawning aggregations and provides an additional perspective on the repercussions of their overexploitation.

Nassau grouper Epinephelus striatus are a large bodied, top level predator that is ecologically important throughout the Caribbean. Although typically solitary, Nassau grouper form large annual spawning aggregations at predictable times in spe- cific locations. In 2003, The Cayman Islands Marine Conservation Board established protection for a newly rediscovered Nassau grouper spawning aggregation on Little Cayman, British West Indies. The large size of this aggregation provides a unique oppor- tunity to study the behavior of Nassau grouper on a relatively intact spawning aggregation. During non-spawning periods Nassau grouper display a reddish-brown-and-white barred coloration. However, while aggregating they exhibit three additional color phases: "bicolor", "dark", and "white belly". We video sampled the population on multiple days leading up to spawning across five spawning years. Divers focused a laser caliper equipped video camera on individual fish at the aggregation. We later ana- lyzed the video to determine the length of the fish and record the color phase. Our observations show that the relative proportion of fish in the bicolor color phase increases significantly on the day leading up to the primary night of spawning. The increase in the proportion of the bicolor color phase from 0.05 early in the aggregation to 0.40 on the day of spawning suggests that this color phase conveys that a fish is behaviorally and physiologically prepared to spawn. Additionally, 82.7% of fish exhibiting dark or white belly coloration early in the aggregation period suggests that these color phases are not only shown by female fish as was previously posited (Current Zoology 58 (1): 73-83, 2012). Keywords Nassau grouper, Epinephelus striatus, Spawning aggregation, Nuptial coloration, Spawning behavior

Many spawning aggregations of marine fishes have been fished beyond the point of sustainability, leading to increased calls for protection through seasonal and/or site-specific fishery closures. Once a closure has been put in place, monitoring the aggregation is imperative in order to learn whether protection leads to the recovery of the population. Current methods for monitoring the status of spawning aggregations rely largely on counts, either subsample or census, usually combined with capturing a subset of the fish to assess individual traits such as length and weight. Handling fish during the spawning aggregation can be stressful for the fish, and can ultimately lead to decreased spawning success, increased susceptibility to predators, or increased mortality through capture trauma or infection. Here we present a novel analysis for monitoring fish on a spawning aggregation that does not require the capture and handling of fish. Following a recovering aggregation of Nassau grouper (Epinephelus striatus) over seven spawning seasons, we show that length-distribution data can be collected by divers using a video-based system with parallel lasers calibrated to a specific distance apart, and subsequently use those data to monitor changes in the size distribution over time. We detected recruitment of new fish to the grouper spawning aggregation in the fourth year of monitoring. In addition to tracking size distribution trends over time, the length distribution information could be combined with an established length-weight regression and an estimate of total abundance to estimate spawning stock biomass. We qualitatively cross-validate this method with census data to evaluate its effectiveness in monitoring the recovery or decline of aggregating species that can be visually observed. (C) 2012 Elsevier Ltd. All rights reserved.

1 Reef Environmental Education Foundation (REEF) Pacific Coast Office, 4726 38th Ave NE, Seattle, WA 98105 Coastal Ecology & Conservation Research Group U.S. Geological Survey, Center for Aquatic Resource Studies, 7920 NW 71st St., Gainesville, FL 32653 3 Department of Environment, Cayman Islands Government, P.O. Box 486GT, Grand Cayman, Cayman Islands Department of Fisheries and Wildlife, 104 Nash Hall, Oregon State University, Corvallis, OR 97331

The Nassau grouper spawning aggregation off the west end of Little Cayman, Cayman Islands was monitored for five consecutive years (2002-2006). An aggregation of approximately 2,000 Nassau grouper (Epinephelus striatus) appears to be stable over the last three years of the study period. Over five years, times of peak numbers of Nassau groupers ranged from one to five days after the full moon (January or February). Nearly 300 spawning bursts were recorded over the study period. On average, spawning bursts were recorded 21 minutes before sunset to 11 minutes after sunset, but were observed as early as an hour before sunset to 20 minutes after sunset. The timing and number of spawning bursts were variable each year. All spawning bursts were observed in the months of January or February. Spawning periods ranged from three to six days in duration and ranged in moon phase from one day after the full moon to eight days after the full moon. The month for the major spawning event appeared to be influenced by the date of January's full moon. Late January full moons (occurring 30 days or more after the winter solstice) resulted in major spawning events in January. Conversely, early January full moons resulted in major spawning events in February. Currents were slack or negligible during nights of spawning. Over a period of 24-48 hours and during sunset dives, prior to the first spawning night, the percentage of Nassau groupers in the bicolor phase increased to 80%, at which time spawning occurred. This shift in color phase may be used to predict when spawning will occur. The formation and the physical location of the Nassau grouper aggregation had low variability throughout the monitoring period. Aberrant colorations of individual Nassau groupers were observed at the study site. Subsequent sightings both on and off the spawning site suggests permanent anomalous pigmentation that was useful for tracking inter-year survivorship. Twenty-one other fish species displaying spawning coloration or behavior were recorded at the site.

Attacks by the isopod Excorallana tricornis tricornis on Nassau grouper Epinephelus striatus caught in Antillean fish traps around Little Cayman Island, Cayman Islands, are recorded. Divers reported heavily parasitized fish during the study period, suggesting that trapping did not exclusively precipitate parasitism. Parasitic infestations were reported to be common in Nassau grouper immediately following their spawning season in mid‐winter.