3.3. Invertebrate Fishery

3.3.1. General description

The invertebrate community is very important to the overall ecology of the LSJRB. It is also important economically for commercial and recreational fisheries. Commercially harvested invertebrates in the lower basin include blue crabs, bait shrimp, and stone crabs. Of the five counties studied (2007-2016), Duval County generally reported the highest catch of crabs (mean 575,002 lbs per year; 170,315 ± SD lbs per year). Recreational fisheries in the area are probably significant for the species mentioned although the level of significance is unclear since there are few reports on recreational landings.

3.3.2. Blue Crab (Callinectes sapidus)

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http://www.jacqueauger.com/…/natural/blue_crab.jpg

3.3.2.1. General Life History

The blue crab (FWRI 2013a) is a very common benthic predator that inhabits estuarine and nearshore coastal habitats in northeast Florida. They are general feeders (omnivores) that will eat fish, aquatic vegetation, molluscs, crustaceans, and worms (FWRI 2002). In the St. Johns River, they reproduce from March to July and then again from October to December (Tagatz 1965; Tagatz 1968a; Tagatz 1968c). Females carry fertilized eggs and migrate towards the more marine waters near the mouth of the river where they will release their eggs into the water. At this point, the young are called zoea, and they drift and develop along the continental shelf for 30-45 days. Wind and currents eventually transport the larger megalops larvae back to the estuarine parts of the river where they will settle in submerged aquatic vegetation (SAV) that serves as a nursery for them. Within 6-20 days of landing at this location, the young will molt and become what is recognizable as a blue crab. In 12-18 months, young crabs will then become sexually mature, ultimately reaching a width of eight inches.

3.3.2.2. Significance

Blue crabs are very important in both the benthic and planktonic food webs in the St. Johns River. They are important predators that can affect the abundance of many macroinvertebrates, such as bivalves, smaller crabs, and worms. They are also important prey for many species. Smaller crabs provide food for drum, spot, croaker, seatrout, and catfish, while sharks and rays eat larger individuals.

A strong recreational blue crab fishery exists, although there are relatively few data on it. The blue crab fishery is the largest commercial fishery in the LSJRB (Figure 3.1). In 2014, it accounted for over 68% of commercial fisheries in the river with 1,124,387 lbs harvested. Duval County reported the highest number of crab landings (451,875 lbs), followed by St. Johns (378,749 lbs), Putnam (174,098 lbs), Clay (119,665 lbs), and Flagler County (16,631 lbs in 2013, but none reported for 2014.)

3.3.2.3. Data Sources

Blue crab data were collected from commercial reports (1994 to 2015) of landings made to the state and research (2001-2015) from the FWRI. The 2014 data are finalized, whereas the 2015 data are considered preliminary.

3.3.2.4. Limitations

The primary limitation with the commercial landing data is that it does not account for young crabs that are too small to be harvested. Additionally, there may be uncertainties regarding location of where the crabs are collected. For instance, fisherman (crabbers) landings reports are made from their home counties, although it is uncertain what part of the river the crabs were actually caught. Changes in harvesting regulations through the years limit what can be said of landings between certain time periods. In this report, total landings are graphed. However, in order to best assess comparison of landings over the years, landings per trip are calculated, and trends investigated using Kendall tau analysis. In terms of the FWRI collection methods assessed in this study, the subsequent data are likely to not have caught the complete size range of crabs that exist within the river.

3.3.2.5. Trend

Commercial landings of blue crabs have been variable, but trending downward for north and south sections of LSJR from 1986 to 2016 (t = -0.230; p = 0.035; n = 31). However, from 2011 to 2012, landings increased more than over the past decade, but decreased sharply from 2013-2016 (Figure 3.20). Additionally, more landings occur in the southern versus northern section of the river (Appendix 3.3.2a). There was a significant decrease in the amount of blue crabs landed per trip over time for the north section of the river (1986-2016) (t = -0.351; p = 0.003; n = 31), but no significant trend for the south (t = 0.148; N.S.). From 2007 to 2016, no significant trend was observed in landings, however, catch per trip increased in the whole river (t = 0.556; p = 0.013; n = 10), but decreased in the norther section of the river (t = -0.733; p = 0.0016; n = 10). There was a significant percent reduction in landings for blue crabs over all during the past decade (t = -0.644; p = 0.0047; n = 10) (65% in 2016) compared to an average of 75% (range 61-86%).

Figure 3.20
Figure 3.20 Commercial landings (in lbs.) of blue crabs within the lower basin of the St. Johns River from 1986 to 2016 (FWRI 2017a).

The FWRI data set shows consistent trends in abundance from 2001 to 2015 (Figure 3.21). Kendall tau correlation analyses revealed no temporal trend in number per set for juvenile (t = -0.067; N.S.), or adult crabs (t = -0.01; N.S.) From trawl catch data, the abundance of juveniles seems to peak in June and is lowest in November (Appendix 3.3.2b). Blue crabs were sampled from January to December with 23.1 m seines and 6.1 m otter trawls both with a mesh size of 3.2 mm. Carapace width (CW) size classes used follow the FIM Annual Report (FWRI 2017b). Blue crabs were caught in zones C, D, E, and F. Adult crabs are usually sampled with 183 m haul seines (mesh size 38 mm), but since mature crab numbers were higher in the otter trawls, this data was analyzed instead. In addition, some individuals classified as adults may still have been reproductively immature due to individual variation in growth rates and timing of maturity (Brodie 2016).

Figure 3.21
Figure 3.21 Number of juveniles and adults of blue crabs caught within the lower basin of the St. Johns River from 2001-2015. The N value indicates the total number of sets completed for the time period (FWRI 2016b). Blue crabs were sampled from January to December with 23.1 m seines and 6.1 m otter trawls both with a mesh size of 3.2 mm. Carapace width (CW) size classes used follows the FIM Annual Report (FWRI 2016b). Blue crabs were caught in zones C, D, E and F. (Figure 3.2 Sampling Zone Map).

3.3.2.6. Current Status & Future Outlook

The blue crab commercial fishery continues to be the premier invertebrate fishery within the LSJRB. The recreational fishery is also likely to be very large, although there is no information available on it.

While common within the river, there is uncertainty regarding whether blue crabs are being overfished or not in Florida. This uncertainty is because the maximum age of blue crabs in Florida is not known. Maximum age is one component that is used in a stock assessment model. Depending on the value used, it can affect whether the model suggests crabs are overharvested or not (Murphy, et al. 2007). Consequently, this piece of information is needed to more accurately assess blue crab stocks in Florida. Currently, there is no required license to fish recreationally using five or fewer traps. In the St. Johns River, five or fewer traps can be used to recreationally catch blue crabs throughout the year (ten gallons whole per harvester per day) except from January 16th to 25th on even years. Crabs can also be caught using dip nets, crab pots, and hand-lines. It is not against the law to harvest non-egg bearing females; however, since female crabs are critically important to ensuring the survival of subsequent generations of crabs, releasing them helps the fishery to be more sustainable in the future. While male crabs can reproduce many times, females only mate once when mature and can store sperm for several months before actually spawning eggs (FWC 2017d).

“If a mature female is harvested, though she may not exhibit eggs, there is no certainty that she has spawned” (FWRI 2017a).

The statistical analysis did not reveal any significant trend in the FWRI data for adults and Young of Year crabs. Commercial catch data indicated a decreasing trend overall (north/south sections of the river combined) and just in the north section of the river; no significant trend occurred in the southern section where most crabs are harvested. Taking everything into account, the current STATUS of blue crab is uncertain, and the TREND is uncertain.

3.3.3. Penaeid shrimp – White, pink, & brown (Litopenaeus setiferus, Farfantepenaeus duorarum & F. aztecus)

shrimp

3.3.3.1. General Life History

There are three penaeid shrimp species that exist within the estuaries and nearshore waters of the northeast Florida region. They are the white, pink, and brown shrimp. The white shrimp is the most common species in local waters. All three are omnivorous feeding on worms, amphipods, molluscs, copepods, isopods and organic detritus. White shrimp reproduce during April to October, whereas pink and brown shrimp can spawn year round (FWRI 2007). However, peak spawning for brown shrimp is from February to March and from spring through fall for pink shrimp. All species spawn offshore in deeper waters with larvae developing in the plankton and eventually settling in salt marsh tidal creeks within estuaries. From there, young will develop for approximately 2-3 months. As they get larger, they start to migrate towards the more marine waters of the ocean where they will become sexually mature when they reach lengths between 3-5 inches. While they generally do not live long (a maximum 1.5 years), they may reach maximum lengths of up to seven inches.

3.3.3.2. Significance

Penaeid shrimp are very important in both the benthic and planktonic food webs in the St. Johns. They are important predators that can affect the abundance of many small macroinvertebrates (see list above). They are also important prey for many species. As smaller individuals such as post-larvae and juveniles, they provide food for sheepshead minnows, insect larvae, killifish, and blue crabs. As adult shrimp, they are preyed on by a number of the finfish found within the river.

The LSJR supports both recreational and commercial shrimp fisheries. The recreational fishery is likely to be large although there is relatively little information on it. In contrast, the commercial shrimp fishery is one of the largest fisheries in the region. However, most shrimp obtained for human consumption are caught by trawlers offshore. Commercial trawling in the LSJR represents a much smaller fishery.

3.3.3.3. Data Sources

Penaeid shrimp data were collected from commercial reports made to the state (1986 to 2015). These comprised of total bait shrimp landings that were generally collected within the river. These data likely include white, brown, and pink shrimp, although their relative proportions are unknown. Data for only white shrimp were also collected and assessed from research (2001-2016) from the FWRI.

3.3.3.4. Limitations

The primary limitation with the commercial landing data is that there are uncertainties regarding the location of where shrimp are collected. For instance, shrimp fisherman landings reports are made from their home counties, although it is sometimes uncertain what part of the river shrimp were actually caught in. Additionally, changes in harvesting regulations through the years may limit what can be said of landings between certain time periods. In this report, total landings are graphed. However, in order to best assess comparison of landings over the years, landings per trip are calculated and trends investigated using Kendall tau analysis. In terms of the FWRI data set, the collection methods assessed in this study may not have caught the complete size range of shrimp that exist within the river.

3.3.3.5. Trend

The commercial total landings of bait shrimp (1986-2016) have been variable with a downward trend in the southern section of the river (Figure 3.22). However, from 2001 to 2012, there have been drastic fluctuations among the years with peak landings occurring in 2004. Less fluctuation has occurred in recent years, but the catch per trip has also decreased significantly (t = -0.422; p = 0.045; n = 10) particularly in the north section of the river where more bait shrimp are reported versus southern sections of the LSJR from 2007 to 2016 (Appendix 3.3.3a).

Figure 3.22
Figure 3.22 Commercial landings (in lbs) of bait shrimp within the lower basin of the St. Johns River from 1986 to 2016 (FWRI 2017a).

The FWRI data set shows consistent trends in abundance for white shrimp from 2001 to 2015 (Figure 3.23). Kendall tau correlation analyses revealed an increasing trend in the number of YOY white shrimp captured per set from seines (t = 0.448; p = 0.01; n = 15) and trawls (t = 0.429; p = 0.01; n = 15). The highest numbers of small white shrimp were encountered in the river from May to August (Appendix 3.3.3b). With seines, nearshore abundance was seen in zones C and D, and fewer numbers occurred in E and F. In contrast, with trawls, a high number was seen in all 4 zones (Swanson 2016).

Figure 3.23
Figure 3.23 Number of juveniles of white shrimp caught within the lower basin of the St. Johns River from 2001-2015. The N value indicates the total number of sets completed for the time period (FWRI 2016b). White Shrimp were sampled from May to August with 23.1 m seines and 6.1 m otter trawls both with a mesh size of 3.2 mm. White shrimp were caught in zones C, D, E and F depending on the gear type used. (Figure 3.2 Sampling Zone Map).

3.3.3.6. Current Status & Future Outlook

Commercial harvesting of penaeid shrimp for bait is a relatively small fishery in the LSJR. The recreational fishery is probably moderately sized, although there are no available data about it. Generally, penaeid shrimp are very abundant in the region. They may be at slight risk of being overfished in the south Atlantic region (see FWRI 2008d for a review). However, the South Atlantic Fishery Management Council, and Gulf of Mexico Fishery Management Council have established fishery management plans for shrimp to try to ensure they are not overharvested (FWRI 2008d). Recreational shrimping regulations include no size limit; however, there is a bag limit of five gallons (heads on) per person each day and a possession limit of no more than five gallons (heads on) per vessel at any time regardless of the number of people onboard. Allowable harvesting methods that comply with the FWC regulations include dip net, cast net, push net, one frame net, or beach sein. The season is closed during April and May in Nassau, Duval, St. Johns, Putnam, Flagler, and Clay Counties (FWC 2017d).

Statistically, there appears to be an increasing trend in Young of Year shrimp. However, commercial data indicated no trend overall and high annual variability. Most shrimp are caught in the northern section of the river. This section has a decreasing trend for catch. However, the southern section of the river also exhibited a decreasing trend in catch.

Taking everything into account, the current STATUS of shrimp is uncertain, and the TREND is uncertain.

3.3.4. Stone Crabs (Menippe mercenaria)

stone crab
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3.3.4.1. General Life History

The stone crab is a fairly common benthic predator that inhabits hard bottoms (such as oyster reefs) and grass beds in the northeast Florida area. Stone crabs are opportunistic carnivores feeding on oysters, barnacles, snails, clams, etc. In Florida, stone crabs reproduce from April through September (FWRI 2007). It is unclear where stone crabs sexually reproduce, and females will carry eggs for approximately two weeks before the eggs hatch. The larvae will drift in the plankton and settle and metamorphose into juvenile forms of the adult in about four weeks. In approximately two years, the crabs will then become sexually mature and reach a width of 2.5 inches. They may live as long as seven years.

3.3.4.2. Significance

Stone crabs are important predators and prey in the estuarine community in the St. Johns River. As important predators, they can affect the abundance of many macroinvertebrates, such as bivalves, smaller crabs, and worms. They are also important prey when both young and older. As larvae in the plankton, they are preyed on by filter-feeding fish, larval fish, and other zooplankton. As adults, they are preyed on by many larger predators in the river.

The stone crab fishery is unique in that the crab is not killed. The claws are removed (it is recommended to only take one claw so the animal has a better chance of survival), and the animal is returned to its habitat. While there probably is a recreational stone crab fishery in the area, there is relatively little information on it. The stone crab commercial fishery is relatively new and small in the LSJR. The highest number of claw landings within the river basin likely comes from Duval County. Claw landings from other counties of the LSJR most likely come from collections made in the ICW.

3.3.4.3. Data Sources

Stone crab data were collected from commercial reports of landings made to the State between 1986 and 2016. There were no available recreational landings data.

3.3.4.4. Limitations

The primary limitation with the commercial landing data is it does not account for young crabs that are too small to be harvested. Additionally, there are uncertainties regarding location of where crab claws are collected. For instance, fisherman (crabbers) landings reports are made from their home counties although the crab claws may have been collected elsewhere. For stone crabs reported by southern counties of the lower basin, it is more likely that the claws were collected in the Intracoastal Waterway (ICW) than the river itself. Additionally, changes in harvesting regulations through the years may limit what can be said of landings between certain time periods. Total landings are shown in this report. However, in order to best assess comparison of landings over the years, landings per trip are calculated, and trends investigated using Kendall tau analysis.

3.3.4.5. Trend

Commercial landings of stone crabs have been variable despite an increase in the number of deployed traps (FWRI 2002). Peak landings occurred in 1994 and 1997 with generally low landings occurring from 1998 to 2006 (Figure 3.24). From 2007 to 2016 landings have increased although the amount caught per trip has decreased. Most landings were reported by the more southern counties of the LSJRB (Appendix 3.3.4a). However, this is most likely a reflection of crab claws caught in the Intracoastal Waterway of the more southern counties than in the river itself.

Figure 3.24
Figure 3.24 Commercial landings (in lbs) of stone crab claws within the lower basin of the St. Johns River from 1986 to 2016 (FWRI 2017a).

3.3.4.6. Current Status & Future Outlook

Stone crabs are not currently at risk of being overfished but are probably now at a level of landings that is all that can be harvested under current conditions along the Florida east coast (Muller, et al. 2006). To minimize negative impacts from commercial fisherman, the Florida legislature implemented a crab trap reduction program in 2002. Currently, there is a daily limit of one gallon per person, or two gallons per vessel, of minimum-sized 2 ¾-inch claws (tip to elbow) to only be collected during the season from October 15 to May 15. Although it is not against the law to harvest both claws from legal sized crabs, the common practice is to leave one claw intact before returning the crab to the water. As a result, crabs can feed and defend themselves more effectively while re-growing the removed claw (FWC 2017d).

Taking everything into account, the current STATUS of stone crab is satisfactory, and the TREND is unchanged.

Water Quality, Fisheries, Aquatic Life, & Contaminants