Gray Snapper Project Collects Valuable Data on Catch-and-Release Fishing Practices

Researchers collect first catch-and-release mortality data for gray (mangrove) snapper, which will be useful for stock assessment considerations and recommendations for responsible angling practices.

Fish and Wildlife Research Institute (FWRI) scientists have determined hook-and-line fishing trends and catch-and-release mortality rates for gray (mangrove) snapper through a collaborative study with recreational anglers and local fishing guides. By characterizing fishing effort within Tampa Bay and nearshore waters, scientists and resource managers could use these data for future stock assessments and recommendations for responsible angling.

Background

Gray snapper (Lutjanus griseus) reside within Florida’s estuaries during their first several years. Because of extensive fishing pressure on gray snapper, minimum-size and bag limits have been used to prevent overfishing. The effectiveness of minimum-size limits depends heavily on the survival of the released fish. Fishing-related mortality of sub-legal gray snapper reduces the number of individuals that reach harvestable size and maturity. As a result, it’s critical to estimate mortality associated with catch-and-release fishing.

FWRI received federal funding to characterize recreational catch, effort (fishing pressure) and catch-and-release mortality rates of gray snapper captured in Tampa Bay and neighboring nearshore waters. Prior to this project, specific catch-and-release mortality studies targeting gray snapper had never been conducted.

Estimates of catch-and-release mortality rates for gray snapper will be invaluable when fully assessing the effects of fishing on the species’ estuarine and nearshore populations. The following sections detail the results of a two-year cooperative study between scientists and volunteer anglers to characterize hook-and-line effort and catch-and-release mortality of gray snapper.

Hook-and-Line Sampling Results

Researchers conducted hook-and-line sampling each month, targeting reef fish in the lower Tampa Bay estuary (inshore zone) and neighboring Gulf of Mexico waters (nearshore zone) from July 2009 to July 2011 (Figure 1). Volunteer recreational anglers and local professional fishing guides helped scientists catch fish in both inshore and nearshore zones (Figure 2).

 

map of sampling area and sites, caption below

Figure 1. Sampling area for inshore and nearshore hook-and-line trips and
catch-and-release mortality experiments. Triangles indicate fishing sites visited during
monthly hook-and-line sampling and quarterly catch-and-release mortality experiments.

 

anglers fishing for gray snapper, caption below anglers fishing for gray snapper, caption below

Figure 2. Left: Volunteer recreational anglers fishing for gray snapper in the inshore zone.
Right: FWRI scientists and volunteer recreational anglers fishing on offshore fishing trip.

 

Scientists, volunteer anglers and guides fished 578 sites, including natural (e.g., sponges, reefs and ledges) and artificial (e.g., bridge pilings, artificial reefs and wrecks) habitat types commonly used by gray snapper and other reef fishes. Researchers and anglers caught and measured 4,500 fish during the study, including 1,606 from the inshore zone and 2,894 from the nearshore zone.

Several reef fish species were common in both inshore and nearshore waters, including gag, gray snapper, white grunt and red grouper (Table 1). The average size of each species of reef fish caught in nearshore waters was always larger than those caught in inshore waters (Table 1). For example, the average size of gray snapper caught in inshore waters (10.5 inches total length) was almost 5 inches smaller than those caught in nearshore waters (15.0 inches total length).

 

Table 1. The number and average total length of select reef fish caught during monthly hook-and-line sampling in inshore and nearshore waters (July 2009 to July 2011).
 

 

Total Number Caught

Average Total Length (inches)

Species

Inshore

Nearshore

Inshore

Nearshore

Black seabass

22

9

8.1

9.1

Gag

487

439

13.1

17.4

Gray snapper

349

177

10.5

15.0

Gray triggerfish

0

15

-

13.4

Red grouper

105

1148

12.3

14.2

Scamp

0

56

-

13.9

Vermillion snapper

0

51

-

11.1

White grunt

200

545

9.6

11.8

 

Habitat type contributed to differences in reef fish catch rates during the study. Catch rates of gray snapper in both study zones were slightly higher on artificial habitat compared to natural habitat. In contrast, catch rates of red grouper were significantly higher in natural habitats compared to artificial habitats. Gag did not show a preference between natural or artificial habitats in either zone.

Using hook-and-line sampling, researchers were able to more effectively collect detailed recreational catch and effort data for gray snapper and other reef fishes associated with inshore and nearshore environments. The study provided additional information, including size ranges, seasonal variation, habitat preferences and general condition of the fish when released back into the water. With this information, researchers were able to document variations in fish size over space and time, reflecting the behavior of these species as they grow and mature.

Catch-and-Release Mortality Results 

In addition to monthly hook-and-line sampling, researchers conducted quarterly catch-and-release mortality experiments for gray snapper in both zones. Volunteer recreational anglers and professional fishing guides also aided FWC scientists in conducting these experiments, which were designed to determine catch-and-release mortality rates.

Each angler was categorized by experience level (beginner, intermediate, or advanced), based on their responses to a survey. Anglers used spinning or baitcasting reels with standardized light to medium tackle, non-offset circle hooks (2/0 and 5/0) and natural baits (live or dead) to catch the fish. In addition to location information, fishing gear specifics and angler experience, researchers also recorded the following relevant parameters for each fish caught: 

  • fish length
  • plastic dart tag number used for identification (Figure 3)
  • hook position
  • fight time
  • handling time
  • observed barotrauma (physical responses, such as inflated swim bladders and bulging eyes, caused by changes in pressure when fish are caught in deep waters)  
tagging fish, caption below fish in holding pen, caption below 

 Figure 3. After tagging (left), researchers placed gray snapper in a holding pen (right).

 

FWRI scientists held each caught fish in a submerged net pen or cage for 48 hours to determine short-term mortality rates (Figure 4 and 5). After 48 hours, researchers retrieved the fish, assessed their condition and released those that survived. Fish that did not survive were placed on ice and returned to the lab for detailed health evaluations. Catch-and-release mortality experiments indicated mortality rates for gray snapper were relatively low. Anglers caught 247 gray snapper during nine inshore and nearshore experiments; 17 of these fish died within 48 hours. The inshore mortality rate (1.4 percent) was lower than the nearshore mortality rate (14.4 percent), and the overall mortality rate (6.9 percent) was relatively low compared to previous reef fish mortality studies. The average size of gray snapper caught in nearshore waters (15.2 inches total length) was larger than in inshore waters (10 inches total length) (Figure 6).

 circular net pen used to hold inshore fish for monitoring, caption below

Figure 4. Gray snapper caught during inshore mortality experiments
were placed in a net pen and monitored for 48 hours.

 

cage used to hold nearshore fish for monitoring, caption below

Figure 5. Gray snapper caught during nearshore mortality experiments were
placed in a cage, sent to the bottom and retrieved after 48 hours.

 

 bar graphs show length frequency for different sizes of gray snapper caught in inshore and nearshore water, caption below
Figure 6. The graphs represent the length frequency for different sizes of gray snapper collected during catch-and-release mortality experiments in Tampa Bay inshore and nearshore waters, 2009-2011. The state (10 inches total length) and federal (12 inches total length) legal limits are denoted by vertical lines. This figure shows the smaller fish in inshore waters migrating to deeper nearshore waters. All mortalities were over the state and federal legal limit.
 

 

Hook position and increasing water depth significantly influenced a fish’s probability of mortality, but other factors, such as angler experience, did not. Gray snapper hooked in the lip were most likely to survive the catch-and-release event, while fish hooked in the esophagus (throat) were the least likely to survive. Necropsies determined the majority of injuries were either esophageal, gill or heart trauma, and only a single mortality was attributed to barotrauma (Figure 7). Most gray snapper that died exhibited trauma linked to being hooked in the esophagus. The majority (90 percent) of fish caught was hooked in the lip, and these fish had a high rate of survival.

 

three different examples of fatal hook trauma and stomach barotrauma, caption below

 Figure 7. Examples of hook trauma determined by necropsy: A) heart trauma;
B) esophageal trauma; C) gill trauma. D) other related trauma: barotrauma.

 

Specific mortality rates are necessary for more precise stock assessments of reef fish species. The short-term mortality rates calculated during this study are relatively low, but are conservative estimates because of the responsible handling practices used. The mortality rate may increase depending on the depth from which the fish is caught and the injuries it sustains from hook placement.

 

Summary 

Through hook-and-line sampling and catch-and-release mortality experiments, FWRI researchers collected data for future stock assessments and recommendations for responsible angling. By working with recreational fishing guides and volunteer anglers, researchers also accomplished the following three important measures: 

  • incorporating the variability in fishing expertise needed to accurately calculate catch-and-release mortality estimates applicable to the recreational fishery
  • involving stakeholders (anglers) in research
  • encouraging the understanding and promotion of scientific research and its role in managing and maintaining fishery populations

Biologists can use tag returns from gray snapper and other reef fish caught during hook-and-line sampling to estimate the long-term survival of released fish. The short-term observations of this study showed that catch-and-release fishing, though an effective management tool for reducing take, can contribute to cryptic mortality, which refers to fish that die unobserved after having been caught and released, especially in deeper waters.

This project was supported in part by proceeds from State of Florida saltwater recreational fishing licenses and funding from the Department of Commerce, National Oceanographic and Atmospheric Administration, National Marine Fisheries Service and Cooperative Research Program grant number NA09NMF4540136.



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