More Than Just a Spawning Location: Examining Fine Scale Space Use of Two Estuarine Fish Species at a Spawning Aggregation Site

Abstract

Many species that provide productive marine fisheries form spawning aggregations. Aggregations are predictable both in time and space and constitute nearly all of the reproductive activity for these species. For species that spend weeks to months on spawning aggregation sites, individuals may need to rely on a forage base at or near the spawning site to balance the high energetic cost associated with reproduction. Here, we ask: do spawning fish with protracted spawning seasons use spawning aggregation sites more or less than adjacent foraging habitats? To answer our research question, we tracked 30 Snook (Centropomus undecimalis) and 29 Spotted Seatrout (Cynoscion nebulosus) at a spawning site during the 2007 spawning season in Tampa Bay (FL, U.S.) using acoustic telemetry. We quantified the amount of time both males and females of both species spent in various habitats with network analyses. Surprisingly, results from network analyses revealed that receivers with the highest edge densities for Snook and Seatrout occurred within the seagrass habitat, not the location of spawning. Likewise, we found that both Snook and Seatrout during the spawning season were using the seagrass habitat near the spawning site as much, or more than the location where spawning occurs. Our results show that if protected areas are formed based on only where spawning occurs, the reproductive stock will not be protected from fishing. Further, our results suggest that spawning aggregation sites and areas surrounding used by fishes, may have multiple ecological functions (i.e., larval dispersal and energy provisioning) that may need to be considered in conservation actions. Our case study further supports hypotheses put forth in previous work that suggest we must consider more than just spawning sites in protected area development and ecological conservation.Keywords: network analysis, spawning aggregation sites, common Snook, spotted Seatrout, Tampa Bay, Florida Boucek et al. Spatial Networks at Spawning Sites INTRODUCTIONMany species that provide productive marine fisheries form high-density spawning aggregations (Beets and Friedlander, 1998;Secor, 2015). Spawning aggregations are defined as group of conspecific fish, gathered at a specific site and time for the purposes of spawning, with fish densities significantly higher than densities found during the non-reproductive period (Domeier and Colin, 1997). Aggregations are predictable in both time and space and can constitute nearly all of the reproductive activity for some species (Domeier and Colin, 1997). At the same time, the spatial-temporal predictability of spawning aggregations, and extremely high catch rates associated with aggregation fishing, often result in these sites being fished to exhaustion once they are discovered (Sala et al., 2001). When these spawning aggregations reach a low-density threshold of individuals where reproduction there ceases to contribute to the population, the fishery associated with that stock often crashes (Sadovy and Domeier, 2005). Given the biolo...

Estimating site-specific spawning parameters for a spawning aggregation: an example with spotted seatrout

“…Therefore, site fidelity at this spawning aggregation indicates that individuals are leaving the site and re turning to spawn at a later time. This temporal movement within the season may be driven by risk avoidance or foraging behaviors (Claydon et al 2012, Becker & Suthers 2014, Boucek et al 2017. The results of inter-seasonal site fidelity over 3 spawning seasons were similar to those seen in 2005, when the spotted seatrout spawning season at Bunces was truncated due to a red tide ).…”

“…Spotted seatrout have traditionally been considered resident spawners that form aggregations within their home ranges and do not migrate to spawn (Walters et al 2007). However, this is not the case at the Bunces FSA site , Boucek et al 2017, which also falls outside of common spawning habitat. Similar behavior has been observed in coral trout, where populations form primary and secondary spawning aggregations (Samoilys 1997).…”

Grouper Tales: Use of Acoustic Telemetry to Evaluate Grouper Movements at Western Dry Rocks in the Florida Keys

“…Grouper movements.-Movements between receiver locations by tagged grouper were compared and examined for hot spots of activity. We used network analysis to create spatial movement graphs, where nodes represented actual locations of receivers and edges represented the movement of fish between these locations (Finn et al 2014;Becker et al 2016;Boucek et al 2017). Node size was proportionate to node degree (the number of edges connecting to the node), and edge width was proportionate to the total number of times fish moved between receivers.…”

Individual consumer movement mediates food web coupling across a coastal ecosystem

“…1c). These designations were based on productivity, salinity, fish community, and geomorphological differences between the two zones (Boucek et al 2017). The movement patterns of individuals with >50% of their detections occurring in upstream sites were classified as upstream snook, and those with more than 50% detections in the downstream estuarine areas were classified as downstream snook.…”

“…1c), while marine prey samples were collected from Florida Bay (three TS/Ph sites; Fig. 1b) over seagrass beds, which serve as important foraging habitat for snook (Boucek et al 2017). All small-bodied fish and decapods (<8 cm total length) were retained for stable isotope analysis.…”