By Meaghan Faletti, USF MS Student
If you’ve ever gone fishing in the Gulf of Mexico – or anywhere around Florida, for that matter – you’ve probably used Pinfish (Lagodon rhomboides) as bait. They work well because many predators consume them as part of their natural diet. This includes nearshore species such as Tarpon, Snook, and Redfish, as well as offshore species such as groupers and snappers. In addition to being used in the recreational fishery, a commercial market exists for Pinfish and extracted over 100,000 pounds of Pinfish from Florida waters in 2016 (NMFS 2018). Furthermore, recreational and commercial landings in the Atlantic and Gulf coasts of the United States show a general increasing trend since 2000 (NMFS 2014). Despite their importance to fisheries, a formal stock assessment has not been conducted for Pinfish.
Figure 1. Pinfish (Lagodon rhomboides)
With Florida’s ever-growing fishing industries, efforts to protect these important food sources are needed to sustain higher trophic-level species that are targeted by the recreational and commercial fisheries, and maintain a natural ecological balance. Not only are Pinfish providing food for predatory fishes, but they also act as a major source of nutrient transfer from nearshore to offshore foodwebs when they migrate to spawn. The nitrogen contribution from Pinfish migration offshore is on the same order of magnitude as trichodesmium, a major nitrogen-fixing bacteria, and one of the most significant contributors of nitrogen to marine systems (Nelson et al. 2013). Due to the importance of Pinfish and other forage (“bait”) fishes, the Florida Fish and Wildlife Conservation Commission (FWC) adopted a resolution in 2017 encouraging further research on these species. The Florida Forage Fish Coalition was then formed to fund this research, and the USF Fish Ecology Lab was chosen as one of the first recipients.
We chose to study the population dynamics of Pinfish in the eastern Gulf of Mexico (eGOM) due to our lab’s familiarity and previous work with this system (Chacin et al. 2016; Stallings et al. 2015) as well as the extensive monitoring previously conducted by FWC’s Fisheries Independent Monitoring program. We chose to focus on four eGOM estuaries that have been sampled monthly with standardized seining methods since 1998: Apalachicola Bay (AP), Cedar Key (CK), Tampa Bay (TB), and Charlotte Harbor (CH). We analyzed density, biomass, and instantaneous growth rates (basically – how many, how big, and how fast are they growing?), and conducted time series analyses to see if these parameters were in synchrony with one another on an intra- and inter-annual basis. We then conducted a Zero-Altered Negative Binomial (ZANB) Model – don’t worry about the name, all you need to know is that it is used to assess what environmental factors may be driving these population patterns.
Figure 2. Four eGOM estuaries of interest where FWC Fisheries Independent Monitoring has conducted seine surveys since 1998. AP: Apalachicola Bay, CK: Cedar Key, TB: Tampa Bay, CH: Charlotte Harbor
We found density and biomass to be highest in CH, followed by TB, AP, then CK. Our time series analysis indicated that AP & CK (two northernmost estuaries) are in sync with one another, and TB & CH (two southernmost estuaries) are in sync with one another. On an intra-annual basis, all four estuaries are in sync with one another, with densities peaking around March-April, and biomass peaking in April-May. This makes sense from a life history standpoint, as Pinfish recruit to seagrass in the spring, and after feeding for a period of time, we expect to see an increase in mass lagging slightly behind the recruitment period.
The ZANB model indicated that density and biomass are significantly related to submerged aquatic vegetation (SAV; e.g. seagrass) for all estuaries. This is likely because seagrass plays an important role for Pinfish by offering protection for juveniles (Chacin & Stallings 2016) and substrata for food as they grow older and begin foraging on epiphytic algae. Pinfish abundance is related to salinity and temperature, which also affect seagrass, so this could either be through direct or indirect effects.
Figure 3. Mean inter-annual Pinfish A) density and B) biomass for 1998-2016. Light gray dotted line represents the overall mean.
Figure 4. Intra-annual Pinfish A) density and B) biomass for 1998-2016. Biomass peak lagged ~1month behind density peak.
Figure 5. Pinfish growth plots. A) Instantaneous Growth Rate (IGR) for each estuary. B) Mean Pinfish standard length (SL) by month. Month 0 represents the average size of the smaller cohort present in month 12 of the previous year.
It is important to understand baseline population dynamics of fisheries species, including forage fish, so that we can better understand the effects of commercial and recreational fishing. This is especially true for species that do not have formal stock assessments such as Pinfish. This information has been shared at the Florida Chapter Meeting of the American Fisheries Society (Haines City, March 2018), the 2nd Florida Forage Fish Workshop (St. Petersburg, April 2018), and will be presented to the FWC Commissioners during a 2018 Commission Meeting. The project has also attracted a wealth of media coverage due to the importance of Pinfish and concerns from stakeholders about potential overharvest. We plan to publish a peer-reviewed article on these data in the summer of 2018 and intend for this information to be used to help better manage Pinfish populations.
References:
Chacin, D. H., T. S. Switzer, C. H. Ainsworth, and C. D. Stallings. 2016. Long-term analysis of spatio-temporal patterns in population dynamics and demography of juvenile Pinfish (Lagodon rhomboides). Estuarine Coastal and Shelf Science 183:52-61.
Nelson, J. A., C. D. Stallings, W. M. Landing, and J. Chanton. 2013. Biomass Transfer Subsidizes Nitrogen to Offshore Food Webs. Ecosystems 16:1130-1138.
NMFS 2018 Commercial landings species locator. https://www.st.nmfs.noaa.gov/pls/webpls/FT_HELP.SPECIES
NOAA NMFS Marine Recreational Information Program, http://www.st.nmfs.noaa.gov/; National Marine Fisheries Service, accessed 4 March 2014
Stallings, C. D., A. Mickle, J. A. Nelson, M. G. McManus, and C. C. Koenig. 2015. Faunal communities and habitat characteristics of the Big Bend seagrass meadows, 2009–2010. Ecology 96:304-304.
Acknowledgments:
Florida Forage Fish Research Program funded by the Florida Forage Fish Coalition (www.floridaforagefish.org). We thank the Florida Fish and Wildlife Research Institute Fisheries Independent Monitoring Program for field collections, and Ian Williams, Aleksandra Cison, and Kiara Barbarette for lab assistance. We also thank Ethan Goddard for assistance with the mass spectrometer.
Funding Sources:
