3.1. Multispecies Reef Fish Fisheries
In the SEUS, groupers form part of diverse multispecies reef fish fisheries composed of species with varying life histories and exploitation histories. These fisheries provide year-round harvest opportunities for fishers as managed species have varying temporal management measures (e.g., seasonal closures). Due to non-selective (or low selectivity) fishing gear and the diversity of species sharing reef habitats, avoiding species closed to harvest is difficult, resulting in high levels of bycatch and mandatory discards. The latter induces discard mortality, which results from depredation, physical injury, or handling stress [
21]. This source of mortality not only undermines minimum size limits but can also prevent meeting stock rebuilding targets. For example, the high discard mortality observed in GOM Gag has been linked to preventing stock rebuilding and potentially inducing recruitment overfishing [
22].
Discards can be considered a significant source of mortality in groupers as many species are associated with deeper waters either throughout ontogeny (e.g., deepwater groupers) or during adult stages (e.g., Gag), which have been linked to increasing physical injuries (e.g., barotrauma) [
23]. The MSA National Standard 9 mandates that bycatch and discard mortality be minimized, however, this has proven extremely difficult to achieve in the SEUS reef fish fisheries. It is worth noting that significant efforts have gone into understanding the mechanisms of discard mortality [
24,
25,
26] and increasing public awareness of the utility of descender devices to mitigate discard mortality (
https://returnemright.org/). Recent management changes have made it a requirement for GOM and SA reef fish fishers to carry a descending device on board [
27,
28].
A substantial increase in recreational effort has been observed across the GOM and Atlantic coasts in the last 40 years (
Figure 2). In addition, increases in recreational landings have been reported for both the GOM and SA [
29]. Due to recreational sector characteristics, such as large user group size and open access nature, recreational data contain much higher uncertainty than that of a commercial sector with mandatory reporting requirements, as observed in the GOM commercial grouper fisheries. Consequently, uncertainty in landings can increase as the recreational sector becomes more relevant unless recreational data collection programs continue to improve. Recent explorations of management strategies to rebuild the SA Red Snapper stock suggest that restricting recreational effort in the reef fish fishery could help meet stock rebuilding goals for Red Snapper and associated reef fishes [
30]. Restricting recreational effort continues to be a promising avenue for rebuilding stocks, however, this must be weighed against the socioeconomic benefits that recreational fisheries provide.
Allocations of many SEUS reef fish stocks have changed over time. Increases and decreases in allocation are observed in the recreational and commercial sectors, respectively. This is especially the case for GOM Red Grouper and GOM Gag, which have recently undergone increases in the recreational sector [
31,
32]. As fisheries historically dominated by the commercial sector, these changes have steered commercial stakeholders to legally prosecute NMFS claiming that multiple MSA National Standards are not being met (
https://www.nationalfisherman.com/gulf-south-atlantic/federal-appeals-court-orders-remand-of-red-grouper-allocations). Managing vulnerable groupers within an already complex multispecies reef fish fishery with multiple user groups, discard mortality rates, and growing uncertainty in recreational landings and effort, is a fundamental challenge faced across the region.
3.2. Protogynous Hermaphroditism
Marine reef fishes display diversity in reproductive systems represented by gonochorism, parthenogenesis, and hermaphroditism [
33]. While a variety of these can be observed in groupers, hermaphroditism is most prevalent in species distributed in the SEUS (
Table 1). Specifically, many of these groupers display monandric protogynous hermaphroditism (protogynous hermaphroditism hereafter), where individuals are born as females, reach sexual maturity, and then transition into males (
Figure 3). Environmental variables, local demography, and mortality schedules have been linked to driving/facilitating sex change in this reproductive strategy [
34]. In this section, I’ll discuss how groupers displaying protogynous hermaphroditism, in conjunction with other life history characteristics, are more conducive to being overexploited.
It has long been understood that reproductive output (e.g., egg production) increases disproportionately with size/age in fish populations [
35,
36]. Consequently, fishing-induced size/age truncation has been shown to reduce stock resilience [
37]. As such, significant management efforts are directed at conserving larger/older fish (e.g., using slot limits) to maintain sustainable spawning stock biomass levels. Protogynous hermaphrodites display dome-shaped egg production, meaning the oldest females show a reduction in egg production as energy is reallocated into sexual transition [
38]. Consequently, protogynous hermaphrodites violate the hypothesis of the largest/oldest females having the highest contributions to reproductive output. Instead, size/age truncation in protogynous hermaphrodites severely depletes male sex ratios in naturally female-skewed populations, creating a unique situation of potential sperm limitation.
Decadal-scale declines in the male sex ratios of two SEUS protogynous hermaphrodites (Gag and Scamp
M. phenax) have been documented [
47,
72]. Notably, both groupers display varying degrees of spawning aggregations, and this behavior in conjunction with increasing fishing pressure has been linked to the declines in male sex ratios [
72]. Interestingly, another protogynous hermaphroditic grouper with significant fishing pressure (Red Grouper) has shown comparatively lighter declines in the male sex ratio, and this has been linked to its non-aggregating reproductive behavior [
72]. In addition, a recent study observed low male gonadosomatic indices and milt reserves in Gag, suggesting they could actually be pair spawners, which would limit fertilization rates at low male sex ratios [
47]. Whether this is a trend in other protogynous hermaphroditic groupers across the SEUS remains to be explored.
In response to the reduced GOM Gag population fitness, the Gulf of Mexico Fishery Management Council created two seasonal MPAs in 2000 (Madison-Swanson and Steamboat Lumps) to increase stock size, followed by a third in 2009 (The Edges). Almost 25 years later, the MPAs’ primary goal remains unattained. A recent study concluded that GOM Gag male sex ratio is at a historic low (5% in MPAs and 0% outside of protected areas) [
47]. In addition, this study also reported increases in age at 50% transition to male, which accompanied by the reduced male sex ratio, suggests the male GOM Gag population is aging while experiencing limited recruitment [
47]. Gag sexual transition does not require male presence, thus female groups traveling to shelf break spawning sites can include newly recruited males [
47]. Consequently, fishing pressure inshore/mid-shelf can simultaneously remove females during peak egg production and bottleneck male recruitment. This case study highlights that MPA success can depend on its spatial extent, species’ life history, reproductive strategy, movement ecology, and surrounding context (e.g., fishery behavior and larval dispersal). It is important to note that measuring MPA effectiveness requires doing so at appropriate time frames [
73], and success will be affected by enforcement and compliance [
74].
Across the world, quantitative assessments are used to assess fish stocks and determine sustainable catch levels. A primary goal of these assessments is to determine reference points, such as MSY, fishing mortality at MSY (
FMSY), and stock size at MSY (
BMSY). These require knowledge of stock productivity, which is notoriously challenging to measure [
75]. Stock-recruit relationships can be used to estimate
BMSY. However, there tends to be a lack of reliable data to estimate steepness, the parameter that controls the shape of the stock-recruit relationship and has a strong influence on stock productivity [
76,
77]. Due to the uncertainty in reference points derived from the stock-recruit relationship, reference point proxies, such as quantities of the spawning potential ratio (SPR; the ratio of the fished stock size compared to unfished conditions), are used [
75]. In the SEUS, a 30% SPR value is the most commonly used MSY proxy to derive reference points and is the current regulation for most GOM reef fishes [
78]. However, a recent simulation study indicates that
FMSY proxies of 40% and 50% SPRs are most probable in achieving long-term MSY for gonochoristic and hermaphroditic stocks, respectively [
75]. Due to their complex life histories, protogynous hermaphrodites undoubtedly require conservative management approaches.
Recent efforts have gone into considering MSY proxy values >30% SPR for hermaphroditic grouper stocks across the SEUS. The most recent SA Scamp stock assessment, in which the stock was found to be overfished, used an
FMSY proxy of 40% SPR [
58]. While 30% SPR continues to be the status quo across the region, management is also considering assessment results under higher SPR values by including them in assessment terms of reference. For example, the latest GOM Yellowedge Grouper
H. flavolimbatus assessment used an MSY proxy of 30% SPR, and while the stock was deemed not overfished nor experiencing overfishing, the terminal year displayed the lowest spawning stock biomass value across the assessed period [
79]. Additional projections using an MSY proxy of 40% SPR resulted in Yellowedge Grouper experiencing multiple years of overfishing, and 50% SPR resulted in the stock experiencing overfishing during the terminal year [
80]. While there is no “one size fits all” answer to MSY proxy values, management should consider using SPR values ≥40% for hermaphroditic stocks and completely abandon considering 30%.
Protogynous hermaphrodites provide unique case studies where traditional fisheries management techniques can fall short of providing reliable estimates of stock status. Maintaining female-specific spawning stock biomass is of primary interest when managing fish stocks. However, careful consideration must be given to male-specific spawning stock biomass when assessing protogynous hermaphrodites, as is the case with many groupers across the SEUS [
81]. Many of these groupers are showing historic declines in male sex ratios, which can result in sperm limitation and stock collapse. Efforts are underway to rebuild these stocks by using MPAs and considering conservative MSY proxies in stock assessments. However, these stocks remain among the most challenging to manage and rebuild. Many SEUS hermaphroditic grouper stocks have experienced historic population declines (
Figure 4). Beyond groupers, many reef fishes that support fisheries display protogynous hermaphroditism (e.g., Sparidae and Labridae). Thus, conservative management strategies should be considered for these species while balancing socioeconomic benefits.
3.3. Deepwater Groupers
A significant proportion of SEUS groupers can be considered deepwater species occupying habitats at depths >100m. In the GOM and SA, Yellowedge Grouper and Snowy Grouper are the most harvested deepwater groupers (
Figure 5). Deepwater groupers are especially susceptible to overexploitation as many of them show comparatively higher longevities, which are associated with slower growth, maturity, and transition rates [
59,
60,
62,
66,
71]. Consequently, their lower natural mortality rates suggest comparatively lower productivity and fishing pressure can quickly cause severe population declines [
82]. Additionally, most of these groupers have been confirmed to display protogynous hermaphroditism [
60,
63,
67]. While little is known about their movement ecology, available information suggests many deepwater groupers display high site fidelity and disproportionate densities of individuals can be observed over small spatial footprints [
83].
Like the Red Grouper and Gag fisheries, The SEUS deepwater grouper fisheries have historically been dominated by the commercial sector but are thought to have started during the late 1900s [
5,
79]. Due to their similarity in habitat use, four species are managed under a combined deepwater grouper stock in both the GOM and SA (Yellowedge Grouper, Snowy Grouper, Speckled Hind
E. drummondhayi, and Warsaw Grouper
H. nigritus). Consequently, species-specific landings can vary from year to year without causing any management concerns as long as the stock annual catch limits are not exceeded (
Figure 6). A recent assessment of the GOM Yellowedge Grouper, the most landed species in the GOM commercial deepwater grouper fishery (
Figure 6), found the species not to be overfished nor experiencing overfishing, but to have the lowest observed spawning stock biomass during the terminal year [
79]. Additionally, stakeholder feedback reporting population declines in GOM Yellowedge Grouper suggests it could be due to increased fishing power (e.g., mapping and electric reels) and recreational effort [
84]. This leads to speculate if both of these variables in conjunction with increased harvest restrictions in comparatively “shallower water” reef fishes (e.g., Red Snapper, Greater Amberjack
Seriola dumerili, Gray Triggerfish
Balistes capriscus, and Gag) could be leading to increased deepwater grouper recreational landings and effort. As recreational allocations continue to increase in other groupers (e.g., Red Grouper and Gag), should we expect the same patterns for the deepwater grouper complex? Commercial grouper landings are more accurate and precise, leading to smaller buffers between annual catch limits and annual catch targets than the recreational sector [
32]. Thus, increases in the recreational deepwater grouper landings would likely be associated with increased uncertainty.
As reductions in the GOM Yellowedge Grouper population are evident, how possible is it to observe increased landings in other deepwater groupers, and to what scale? Many of these species have poorly understood life histories, highly uncertain recreational landings, and display decadal-scale overexploitation. Misty Grouper
H. mystacinus and Marbled Grouper are two species distributed across the SEUS for which their population trends are unknown and landings data are scarce. The SA Speckled Hind stock has shown signs of overexploitation since the 1970s, which was followed by reduced bag limits in 1994 [
63]. However, evidence suggests that the stock continued to be overexploited through the 2000s [
63]. Additionally, a recent study reported low population connectivity, limited movement, and high numbers of harvested young fish in the GOM Snowy Grouper stock [
85]. In attempts to help rebuild deepwater reef fishes (including groupers), the South Atlantic Fishery Management Council implemented eight deepwater MPAs in 2009 [
86]. To date, the investigations conducted demonstrate no evidence of the MPAs improving the status of grouper stocks [
87,
88]. In fact, one of these studies found that community composition within the largest of these MPAs has shifted away from groupers to other reef fishes [
88]. Thus, long-term monitoring of MPAs will be important to account for long generation times observed in these long-lived species and to investigate how different fishes respond to the MPA effect.