Note:  The following article was condensed for Careful Catch readers in April 2011 by Maryland DNR Fisheries Biologist Rudy Lukacovic.  The regulations cited were those in effect during the time of the original publication and are not current.  For current fishing regulations visit the Maryland DNR fishing regulations website.

Mortality Rate of Striped Bass
Caught and Released with Artificial Lures
During Spring on the Susquehanna Flats
.

Prepared by
Rudy Lukacovic
and
Ben Florence

Introduction
A catch-and-release fishery has developed for striped bass Morone saxatilis in the upper Chesapeake Bay during the spawning season. Most fishing in this area is concentrated on the Susquehanna Flats, an area above a line from Turkey Point on Elk Neck to Sandy Point on Spesutie Island at Aberdeen Proving Grounds. The Susquehanna Flats are currently included as part of the upper bay striped bass spawning area. Regulations are in effect that prohibit catching, harassing, pursuing, hunting, shooting, wounding or attempting to catch striped bass or striped bass hybrids in this area and other spawning rivers. These restrictions are in effect from March 1 to May 31.
The Susquehanna Flats is an area of low to no salinity, particularly in spring. Release mortality for striped bass in warm water (>25C; 77F) is higher in freshwater (RMC 1990). At temperatures of 16-23.5 C (61-74F) Nelson (1998) showed the mean adjusted mortality for striped bass 293-610 mm (11.5-24 in) was 6.4%. Data concerning the mortality rate of striped bass greater than 610 mm (24 in) caught and released in a low salinity, low temperature environment does not exist.
Controversy has resulted because participants in the fishery believe a legal catch-and-release fishery can exist without adversely impacting striped bass populations or spawning.  Additionally, the prohibition of targeting striped bass is difficult to enforce because it is hard to prove in a court of law that an angler actually intended to catch a striped bass.
A workgroup composed of various stakeholders was formed by Maryland’s Fisheries  Service to meet and discuss the issues regarding this situation. Stakeholders were comprised of recreational and commercial fishermen, Maryland Charter Boat Association representatives, Cecil County Chamber of Commerce members, Maryland Sport Fish Advisory Commission members and Fisheries Service scientists. After two meetings, it was the consensus of this workgroup that the Fisheries Service design and conduct a study to determine the mortality of striped bass associated with catch-and-release fishing under these environmental conditions.

Methods
Charter boats captains, professional guides and experienced local fishermen were hired, or volunteered, to catch striped bass for this study. Two charter boats and two to four smaller vessels were designated to fish for two consecutive days each week of the study. Workgroup members, stakeholders and Department  of Natural Resources personnel caught fish on board the designated vessels. A cross section of fishing experience was represented. Department of Natural Resources-Fisheries Service boats accompanied the fishing boats to transport striped bass to holding pens.
Fishing was restricted to the Susquehanna Flats. Three trials were conducted over a five week period to evaluate the influence of seasonality. The Flats were fished on April 20-21 (Trial I), May 4-5 (Trial II), and May 18-19 (Trial III), 1998. Each trial consisted of two consecutive, single day replicates. Fish from day 1 were held separate from day 2 fish.
Terminal tackle was limited to single hooked artificial lures. Participating anglers used medium action spinning and casting rods equipped with 10-15 pound test line.
If a fish was shallow hooked (defined as hooked in the lip or mouth) it was marked with a    hole punched through the lower lobe of the caudal fin. If a fish was deep hooked (hooked in the gullet or stomach) a hole was punched in the dorsal lobe of the caudal fin. A fish hooked in the gills was marked with two holes in the lower lobe, and a foul hooked fish (defined as hooked externally anywhere posterior to the eyes) had one hole punched in each lobe of the caudal fin. Each fish was placed in a tank on board a transport vessel.
Fish were divided into two groups: greater than or less than 610 mm. Twenty fish of each size group were targeted for each replicate. Any fish in excess of twenty from each size group were measured, sexed, hook location recorded and released. An additional 20 fish from a pound net were to be added to the pen.
On April 20-21 one Fisheries Service vessel was used to transport fish caught by all fishing boats.  Three Fisheries Service transport boats, each assigned to accompany a specific charter boat or group of smaller fishing boats, were used on May 4-5 and May 18-19.
Each transport vessel was equipped with a circular fiberglass tank and oxygen. Upper bay water was pumped into the tanks and was kept oxygenated to ambient levels. Once 10 to 15 fish were captured, they were taken to holding pens. Water in the tank was exchanged between each trip.
Fish were placed in floating net-pens. Net pens were 4.6 m (15 ft) square by 3.7 m (12 ft) deep and were suspended by a floating wood and styrofoam frame. They were anchored in 3.0 m (10 ft) of water. Pens were checked every day for three days.
Each net was emptied after three days of observation. Survivors were released after being measured, sexed and hook location (hole punch position) recorded. Mortalities were discarded after being measured, sexed, if possible and hook location recorded.
Surface and bottom temperature (C), salinity (ppt), dissolved oxygen (mg/l) and pH were recorded at the fishing sites and in the transport tanks several times each day of fishing. These parameters were also recorded at the pens each day of the study.
Results

During Trial I (April 20-21), a total of 653 fish were caught by all boats participating in the study. Forty nine small fish and 12 large fish were placed in the net-pens (26 on day 1 and 35 on day 2). One female (875 mm), gravid when caught, was among the 61 fish used in the mortality segment. This fish released her eggs while in the net-pen. All others used as part of the mortality segment of Trial I were males. Three fish that were deeply hooked and two that were foul hooked survived. One large shallow hooked male died (8.3% of the large fish; 1.6% of the total). Nine pound net fish were also placed in the nets, 6 on day 1 and 3 on day two. Four pound net fish died (44.4%) during the 72 hour observation periods. Five hundred ninety two fish that were caught and not used in the mortality segment were released.  Total length, sex and hook location were recorded for some individuals.
Water temperatures during Trial I ranged from 13.3-15.8C (57-59F). Dissolved oxygen ranged from 7.85-11.0 mg/L and pH varied from 7.12-7.88. Salinity was constant at 0.0 ppt.
Trial II (May 4-5) caught 912 striped bass. One hundred and nine were used for the mortality portion of the study. Seventeen large fish, including three unspawned females (792-900 mm) were put in the net-pens for this trial. After 72 hours, four mortalities were documented among 92 small fish (4.3% of the small fish; 3.7% of the total). One death occurred among 5 deep hooked fish. The other 3 mortalities were shallow hooked fish. All three females survived and still retained their eggs at release. Two of the three large females had been tagged the previous year by DNR. No fish from pound nets were used in this trial.
Water temperatures in this trial ranged from 15.9-16.6C (61-62F). Dissolved oxygen levels were between 9.58-10.45 mg/L, and pH varied from 7.48-8.27. Salinity was again constant at 0.0 ppt.
One hundred and seven striped bass, out of 344 caught, were put in the net-pens for Trial III (May 18-19). Twenty three of these fish were greater than 610 mm and three mortalities were documented in this size group (13.0%). Fourteen mortalities (16.7%) were counted among the 84 fish less than 610 mm. The mortality combining both groups was 15.9%.  All mortalities were males with the possible exception of one large, 761 mm (30.0″) fish, which was too decomposed to determine sex. Two females were identified by dissection among the small fish. Five females were recorded in the group of larger fish and all still retained their eggs at release. One of seven deep hooked fish died.
Water temperature increased from 17.6C (64F) to 21.9C (71F) during this trial. Dissolved oxygen levels varied from 8.73 to 10.25 mg/L and pH ranged from 7.32 to 8.37. Salinity was constant at 0.0 ppt.
The mortality rate combining all fish for all trials was 7.9%. The mortality rate for the small fish (n=225) was 8.0% and 7.7% for the large fish (n=52).

Discussion

Stress and physical injury are the two major factors that influence survival of fish that are caught and released. Temperature, fish size and salinity are the most influential stress-related factors that affect the survival rate of striped bass that are caught and released (RMC 1990). The physical damage associated with hook injury has been documented as the single most important factor in hooking mortality (Muonke and Childress 1994).
In the study design, fish size, water temperature and hook location were considered variables influencing catch and release mortality. Salinity was constant at 0.0 ppt throughout all three trials and was not considered a variable. Upper bay salinity is usually very low, if present at all, especially during the spring.
Striped bass were grouped as “large” or “small” fish in this study. This designation was based on the lack of hooking mortality data for striped bass greater than 610 mm caught in fresh water (0.0 ppt salinity) at low temperatures (<70F).
In this study eighteen mortalities (8.0%) were documented among fish less than 610 mm (N=225).  There was no significant difference in their mortality rate compared to 52 fish greater than 610 mm. Four mortalities (7.7%) were recorded among the large size group.
Temperature was the only factor affecting fish survival in this study. Nelson (1995) reported an adjusted mortality over five trials of 7.3% for striped bass caught on artificial lures at salinities of 0.0 ppt and temperatures between 16.0-23.5C (60.8-74.0F). Mortality at 16.0C (60.8 F) was 0.0% but rose to 17.6% at 22.0C (71.6F). At a middle temperature of 19.0C (66.2F) mortality was 6.7%.
The total mortality in Trial I of this study was 1.6% at temperatures of 13.8-15.0C (57-59F). During the second trial it increased to 3.7% at 16.2-16.6C (61-62F). Striped bass died at a rate of 15.9% during Trial III with temperatures ranging from 17.6C (63.6F) to a high of 21.9C (71.3F).
Higher temperatures and the rate of temperature change may have worked in combination to exacerbate mortality in Trial III. During Trials I and II, temperatures were low and did not increase appreciably or rapidly during the 72 hour holding period.  The temperature during Trial I (F=1.6%) increased 0.9C (1.5F). Trial II (F=3.7%) increased 0.3C (0.5F). As expected, the temperature during Trial III (F=15.9%) was higher than the other two trials. Trial III also experienced the greatest and most rapid increase in temperature. At the start of fishing on May 18, temperature was 17.6C (63.6F). Temperature increased to a high of 21.9C (71.3F) on May 21, a change of 4.3C (7.7F). It decreased to 20.2C (69.3F) at release on the last day.
The release of water from Conowingo Dam on the Susquehanna River, 4 miles above its mouth, affects the area of the flats where the net-pens were anchored. Pulses of water for power generation from Conowingo pool are drawn from deeper and cooler levels. This appeared to occasionally affect temperatures at the pens.
Hook location did not play a significant role in mortality in this study. Single hooked artificial lures were used to eliminate terminal tackle as a variable. Some participating anglers did use treble hooks, but changed lures when asked.
Fifteen fish (5.4%) were deep hooked among 277 striped bass used in the caging experiment. Two mortalities (13.3%) were documented among deep hooked fish less than 610 mm. Two fish larger than 610 mm were deep hooked and both survived.
Natural baits such as blood worms and cut fish are used in the upper bay to catch white perch Morone americana and channel catfish Ictalurus punctatus and these baits also take striped bass. Increased mortality rates from higher deep hooking frequencies using natural baits have been documented for smallmouth bass Micropterus dolomieu (Clapp and Clark 1989), brook trout Salvelinus fontinalis, brown trout Salmo trutta  and rainbow trout Oncorhynchus mykiss (Shetter and Allison 1955; Stringer 1967), and bluegill sunfish Lepomis macrochirus (Siewert and Cave 1990). However, mortality was not considered significantly different for largemouth bass Micropterus salmoides (Rutledge and Pritchard 1977).
Two field studies which evaluated hook location, fish size and season reported the mortality of deep hooked striped bass caught on bait to be 41% in the fall and 56% in the spring (Lukacovic and Uphoff 1997). During 1995 striped bass were hooked in specified deep or shallow anatomical locations and held under controlled conditions for 60 days at the Cooperative Oxford Laboratory (K. Lockwood, Maryland Fisheries Service, personal communication). Deeply hooked striped bass died about 57% of the time in this experiment. The low deep hooking rate was anticipated because artificial lures were used exclusively to capture fish for this study.
The lower rate of mortality among the deep hooked fish caught with single hooked artificial lures verses those caught with single baited hooks can, in many cases, be attributed to hook orientation. It was not possible to determine hook orientation in every deep hooked fish because of the distance between boats. When such an examination was made the hook was consistently pointed dorsally. The hook was removed from all fish except one that was hooked in the roof of the mouth. This fish, a 620 mm male, with the bucktail still in-situ survived the 72 hour holding period and was vigorous when released.
Necropsies are routinely performed on all dead, deep hooked fish. In the study, which used natural bait on single hooks, the hook was oriented downward in 31 of 40 deep hooked fish. Damage to the heart and/or liver is the most common result and hemorrhage is usually profuse. This damage was easily seen as most fish died within 6 hours and post-mortem change was not severe. In this study with artificial lures, only two deep hooked fish died and no organ damage or sign of hemorrhage was seen in either the abdominal or peritoneal cavities. Mortalities did not float and were not documented until the nets were pursed at the end of 72 hours. Post-mortem changes obscured any subtle focal damage that may have resulted from a single point of penetration.
No “floaters” were seen in the net-pens during any of the trials. Low temperatures may have retarded decomposition and associated gas production. Dead fish were only documented when the nets were pursed at the end of each trial replicate. The current, which was almost constant, billowed the net and may have held some fish down below the surface.  When the mortalities were discarded, all sunk, except some of the fish from Trial III which appeared neutrally buoyant. Post-mortem change was variable among the mortalities in Trial III suggesting that deaths occurred over time. Mortalities that were documented in the spring study, which used baited hooks, all floated. This information is not available for the fall segment.
Pound net fish were used in Trial I. The commercial pound net from which they were taken was 7 miles from the net-pens.  Wind conditions on one of two days that pound net fish were used was severe (20-25 mph). Transportation of pound net fish was so different from hook and line caught fish that no comparison of survival is possible. Their use was discontinued for Trials II and III.
A total of 1909 striped bass were caught during all 3 trials. One hundred and thirteen fish (5.9%) were greater than 610 mm. Two hundred and seventy seven striped bass, 225 small fish, 52 large fish were put in the net-pens. Nine of 52 large fish (17.3%) used in the mortality study were females. Two females (0.9%) were documented among 225 small fish. Expansion of these percentages to all fish caught suggests that 20 of 113 large fish and 16 of 1796 small fish were females.

References

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