Tuesday, March 1, 2016

Fishing for Bedding Bass - Benign Past Time or Cause for Concern?

It’s March, and the signs of spring are popping up everywhere in Florida. Days are longer, temperatures are warmer, and trees are beginning to bud. Birds, flowers, and bees are becoming more active, and with the warming temperatures, underwater activities are heating up too. More specifically, Florida Largemouth Bass (Micropterus floridanus) are beginning to move into the shallows as they seek to begin their spawning season.

If you’re an angler this time of year means the potential to target bass that are both highly vulnerable and readily accessible, with a legitimate shot at landing a big one. This is in large part due to the reproductive biology of Largemouth Bass; they excavate nests in shallow water commonly visible from afar, display parental care (i.e. they protect the young in their nests), and will  attack predators (or lures) that enter their nests. The process of specifically fishing for bass as they defend their brood (eggs and young) is known as bed fishing, and a simple internet search will return hundreds of websites that detail specific baits, techniques, and strategies to target bedding bass (Figure 1). Indeed, bed fishing is a practiced by many and staunchly opposed by many others. At the center of the debate is whether the removal of guarding parents is bad for the overall bass population. Numerous studies have shown that bed fishing can cause individual nests to fail, but does this scale up to the entire population?

Figure 1. One of many websites that provide detailed information on how to catch bedding bass


Bass fishing and Florida have a long and storied history together. With approximately 7,700 lakes, highly productive water bodies, a long growing season, and the genetically distinct Florida Largemouth Bass known for its rapid growth, Florida represents a prime location to grow bass of trophy size. Managers with the Florida Fish and Wildlife Conservation Commission (FWC) have long recognized the high caliber of bass fisheries in the state, and in 2009 they set out to develop a formal plan to ensure that Florida is the undisputed the “Bass Fishing Capital of the World”. The product of these efforts was a 20 year plan, formalized in 2011, that incorporated direct input from avid anglers, tackle shop owners, lure manufacturers, fishing guides, outdoor writers, tournament anglers, university researchers, and tourism destination marketers. The plan details specific goals for the agency to address including habitat, fish, and people management related issues. Interestingly, the second largest concern among Florida stakeholders was the potential effects of bed fishing on bass populations. In other words, is regulation need to protect bedding bass so as to avoid negative population level effects?

Study Design

In response to the concerns of Florida anglers FWC initiated a multi-year study specifically designed to address this issue. Utilizing a series of nine experimental populations at the Florida Bass Conservation Center we created a series of 1 acre ponds that were designed to mimic local area lakes. To each pond we added equal numbers of adult male and female bass (n = 20 total) alongside Bluegill, Seminole Killifish, Eastern Mosquitofish, and Grass Carp (to control aquatic vegetation). Fish such as Mosquitofish were to serve as forage for bass whereas Bluegill were added to serve as nest predators. Fish were stocked at densities similar to historical block net data collected from the Ocklawaha Chain of Lakes. To each pond we added a series of brush piles and cinder blocks to provide adequate spawning habitat (Figure 2). All adult bass were fin clipped (for genetic analysis) and PIT tagged to allow for individual identification. Adult bass were stocked in January and all ponds were drained in the fall. To assess angling impacts on reproduction, five ponds received a fishing treatment and the remaining four were left undisturbed. This experiment was conducted twice, once in 2013 and again in 2014.

Figure 2. One of nine research ponds used to study the impacts of bed fishing on Florida Bass recruitment. Brush piles and cinder blocks were added to ensure adequate spawning habitat was available for bass

Once the spawning season was initiated snorkelers were in the water every other day to monitor spawning activities (Figure 3 - left), and once a nest was identified its fate was tracked (i.e. to determine what percentage of nests were made and of those, how many were successful) (Figure 3 - right). In the fishing treatment, we specifically targeted known nests to illicit a potential bed fishing response. If a fish was captured, we first identified it (via PIT tag) and then placed it into an enclosure within the same pond for one hour. The thought process was the removal of a guarding parent for one hour would maximize the impact of predators on the unguarded nests. With individual catch histories and genetic fin clips we would later be able to relate individual contributions (what adults produced which offspring) and how production rates varied with number of captures.

Figure 3. (Top) Biologists caught ‘mid-snorkel’ attempting to locate and identify all Florida Bass spawning attempts in our experimental populations. (Bottom) A foam float was placed over each identified nests so the fate of individual reproductive efforts could be tracked.

Nine months following population establishment, all ponds were drained and the total number of offspring produced per population was quantified. Additionally, 200 fin clips were randomly taken from juveniles (i.e. fall recruits) for genetic analysis. Using genetic profiles from all adults and a subset of juveniles we conducted parentage analysis in a maximum likelihood framework to figure out which parents produced which offspring. So, for both 2013 and 2014 we had at the end of each field experiment records of: how many nesting attempts occurred, how many nests were successful, how many times each bass in the fished populations were captured, and how many recruits were produced per population. Once back in the lab, genetic profiles and genetic analysis was performed on a total of 3,050 adults and offspring (across both years) to determine how many adults contributed to reproduction, how many offspring were produced per adult, and how these factors varied as a function of fishing treatment.

Results

In all of 2013, we documented a total of 56 active nests, 31 of which were in unfished ponds, the remaining 25 nests in fished populations. In 2014, the number of active nests increased dramatically with a total of 148 being located. Again, more nests (82) were located in unfished ponds relative to fished (66). In terms of the number of nests that were successful (i.e. we observed fry swimming over the nest), success rates were higher in fished populations relative to unfished in 2013, although this difference was not statistically significant. We observed the reverse trend in 2014 (i.e. unfished had significantly higher nest success rates). Combining data from both years together we noted that unfished ponds on average had both a greater number of nests and a higher number of successful nests, although this difference was not statistically different (Figure 4). So, in light of the differences in nest number and success rate, did we observe a greater number of fall recruits in unfished populations?

 
Figure 4. The percentage of nests that were identified as successful for the 2013, 2014, and combined data sets.

Before we look further into how fishing impacted recruitment and parental contributions, it’s important to look out how effective our fishermen were at capturing spawning Florida Bass. In populations in which all spawning activities were identified our most skilled anglers were only able to capture a moderate fraction of the bass that were targeted. Specifically, in year one only 36% of bass were captured, and although our catch rates were higher in 2014, we still only managed to capture 53% of nest tending adults. A number of studies have shown that Florida bass are less likely to strike at the first cast presented to them, and any number of casts for that matter relative to Northern Largemouth Bass. So in this case, it’s unlikely that our anglers abilities were driving the low catch rates, but likely this was an artifact of the difficulties associated with catching Florida Bass.

When we examined recruitment patterns across fished and unfished populations we saw a complete lack of trend. In other words, in 2013 we noted a higher number of recruits were produced in unfished populations; however, in 2014 the exact opposite was true. Important to note was the high degree of variability both within and between years (Figure 5). For example in the first year’s experiment we had one population produce a staggering 3,479 offspring while another produced only 34.

 
Figure 5. The number of fall recruits produced in experimental Florida Bass populations subjected to bed fishing relative to control populations.

Next, in our efforts to examine how bed fishing impacts reproductive efforts in Florida Bass we looked at the number of adults that contributed to reproduction and the average number of offspring they produced. In 2013, both fished and unfished ponds had only a moderate fraction of all adults contribute to reproduction (fished: 27% of adults; unfished: 37.5%), whereas these values were significantly higher in 2014 (fished: 68%; unfished 60%). Thinking that perhaps nest guarding males might be more heavily influenced by angling (as they are more likely to be targeted) we examined the average number of males and females contributing to fished and unfished populations and observed no significant differences. In terms of the number of offspring produced, during the first year of the experiment we observed large numbers of recruits combined with low numbers of contributing adults resulting in a high average number of offspring per adult. The opposite trend was observed in 2014. As with previous results we saw a dramatic shift in average contributions between years but not treatments (Figure 6). In other words, the greatest changes in average number of offspring were observed between years but not treatments. In fact, in year two we observed a greater number of offspring per parent in fished populations relative to unfished.

Figure 6. A boxplot displaying the average number of offspring produced per Florida Bass as a function of sex, treatment (bed fished vs. unfished), and year. Triangles represent mean values, black bars denote median values, boxes identify values falling within the 25th and 75th quartiles, and open circles represent outliers.

The last piece of the bed fishing puzzle involved examining how catch histories impacted reproductive output. Do bass that have been removed from their nest still produce offspring? The answer is yes! In fact in some cases we observed fish that were angled from multiple nests produced higher average numbers of offspring than fish never captured (Figure 7) (Note: fish removed from individual nests via fishing were done so only once such that repeated captures implied multiple distinct spawning events). Does this mean that capturing a bass off the nest is beneficial? Hardly. But it does put to rest the fear that bass that are bed fished are essentially non-contributors to fall recruitment, at least in our study system.

Figure 7. The mean number of offspring produced per adult male Florida Bass as a function of the number of times it was captured from a spawning bed. Dark circles represent mean values and thick black bars represent median values. Sample sizes are listed above capture category.


Conclusions

We created a series of experimental populations that were replicated across years to assess the impacts of bed fishing on Florida Bass and failed to illicit statistically significant differences in the mating success, reproductive success, or overall patterns of recruitment in Florida Bass. The potential for bed fishing to illicit population level responses in recruitment of black basses has been the focus of extensive debate and research for decades and numerous studies have highlighted the negative consequences at the individual level associated with catch-and-release angling. However, it appears many of the individual level impacts fail to scale up at the population level. A long list of potential explanations may serve to observe our observations, including the reproductive biology of Florida Bass, their reduced vulnerability to angling, and the possibility for density-dependence processes and recruitment compensation to drive patterns in fall recruitment.

In the warm Florida climate Florida Bass spawn over a protracted period (January to May) and have been known to spawn multiple times within an individual season. Thus a failure due to nest predation may be compensated for by a success later in the season. We documented a number of cases in both fished and unfished populations in which individuals spawned multiple times. The notion of limited catchability alluded to before may also help to explain our observed trends. That we knew where every spawning attempt was occurring, made directed efforts towards catching all spawning fish, and failed to capture all or most of the fish implies a significant portion of nests will go undisturbed in the wild. In the complex (i.e. high levels of aquatic vegetation) water bodies of Florida it seems unlikely that anglers would be present in sufficient number and consistency to hit all spawning events. Especially if that water body is someplace the size of the St. Johns River (310 miles long) or Lake Okeechobee (710 square miles in surface area). Another potential explanation for the observed trends includes the role of density-dependent recruitment compensation in Florida Bass populations. In other words, lowered population density (i.e. fewer successful nests) associated with bed fishing may be compensated for by increased survival of the remaining offspring. Thus, individual losses may be offset by compensation at the population level.

The Take Home Message

The results from this study suggest that bed fishing may not significantly impact the number of adults contributing to reproduction, the average number of recruits produced per adult, or the total number of offspring produced in Florida Bass populations. Additionally, results indicate that fish captured during the spawning season contributed to fall recruitment despite being removed from their nests. These conclusions do not imply the absence of any negative impacts, as bed fishing that involves a harvest component may illicit responses drastically different than results derived from this experiment. Furthermore, the present study was not designed to measure deleterious impacts associated with selective fishing practices (i.e. targeting trophy bass only). Nonetheless, these results provide important management insights for Florida Bass populations occupying biological and physical environments similar to those studied in this experiment. Moving forward the research results obtained here will be used to ensure the health and success of Florida’s most prized freshwater sport fish populations!

Credits This research was  by conducted by FWC with funding from the Federal Aid in Sport Fish Restoration Act (Wallop-Breaux Act). Nick Trippel (FWC) was responsible for project design, management, and execution. John Hargrove (UF) assisted with field work and completed all genetic analysis (extraction, amplification, parentage assignments). A peer-reviewed publication of research findings will be forthcoming later in 2016!

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