Mortality of Lingcod, Ophiodon elongatus, Related to Capture by Hook and Line – Statistical Data Included
Douglas Albin
Introduction
The lingcod, Ophiodon elongatus, is a large carnivorous fish of the family Hexagrammidae inhabiting the eastern Pacific Ocean from Alaska to Baja California (Miller and Lea, 1972). Its life cycle is entirely marine, with egg masses laid during winter on rocky habitats, typically in areas of surge or current. The male lingcod defends the nest from egg-eating fishes (Low and Beamish, 1978). Larvae and early juveniles are found in pelagic waters during the spring months, while juveniles of about 7-35 cm length inhabit near-shore sandy areas. Larger lingcod are typically found on rocky reefs at depths to 420 m (Miller and Geibel, 1973).
Lingcod are taken in significant numbers by marine recreational and commercial fisheries in California (Fig. 1) and other Pacific coast states (Karpov et al., 1995; PFMC(1)). Management measures for lingcod include bag limits and minimum size limits for recreational fisheries, and catch quotas and minimum size limits for commercial fisheries. A minimum size of 56 cm (22 in) total length was applied to California’s recreational fishery in 1981. In 1998 a limit of 61 cm (24 in) total length was applied to all recreational and commercial fisheries of California, Oregon, and Washington.
[Figure 1 ILLUSTRATION OMITTED]
The portion of captured fish released live from California’s recreational fishery has risen from about 10% in 1981 to about 40% in recent years (Fig. 2). Such high return rates suggested that mortality of released lingcod should be determined and, if significant, should be included in stock assessment estimates of total fishing mortality as recommended by Clark (1983).
[Figure 2 ILLUSTRATION OMITTED]
During the past few decades, a general trend of increasing harvest pressure on fishery resources has given rise to increasing use of fishery management regulations requiring release of some (size limits) or all (catch-and-release only recreational fishing) fish captured. Additionally, many recreational anglers voluntarily return some or all fish captured as a conservation measure.
Muoneke and Childress (1994) reviewed studies, popularly called “hooking mortality” studies, evaluating mortality to fish that are hooked, landed, handled, and released. Most of the studies were conducted in fresh water and pertained to salmonids, centrarchids, or percids; mortality rates ranged from 0 to 88%.
In marine environments, Wertheimer et al. (1989) found a mortality range of 18.5-26.4% for chinook salmon, Oncorhynchus tshawytscha, held 4-6 days after capture by commercial trolling gear. Gjernes et al. (1993) found mortality rates of 30% for chinook salmon and 14% for coho salmon, O. kisutch, held less than I day after capture by recreational anglers. Diodati and Richards (1996) evaluated capture and release mortality of striped bass, Morone saxatilis, by conducting experimental angling in a 2 ha saltwater impoundment; mortality for captured fish was 9% over a 58-day period. At the end of the experiment the impoundment was drained; condition factor was significantly lower in surviving captured fish than in surviving fish that had not been captured. Bugley and Shepherd (1991) estimated capture and release mortality to black sea bass, Centropristis striata, by holding captured fish in wire cages on site for 48 h; mortality was 4.7%.
Ideally, the holding period in a hooking mortality study should last more than a few days because fish captured and released in apparently good condition can expire days later. Delayed mortality can occur from hooking wounds, disease, or osmoregulatory dysfunction (Muoneke and Childress, 1994).
Methods
Our general approach was to capture lingcod using traditional hook and line gear and then hold them in aquaria as long as practical to observe their general condition and the condition of any wounds arising from capture. When a fish became ill or died, we attempted to attribute the illness or death to either a) physical injuries and stress incurred during capture or b) injuries and stress incurred as a result of holding the fish for evaluation.
Monterey County
During 24-29 September 1995, 15 lingcod were captured and held aboard the California Department of Fish and Game vessel RV Mako off Monterey County (Fig. 3). Using sonar, schools of fish were located over rocky habitats at depths [is less than] 50 m. The vessel was then drifted over the schools, and anglers fished with conventional recreational rod and reel gear, mainly with large baits or lures intended to target lingcod. Baits were predominately live market squid, Loligo opalescens; live jack mackerel, Trachurus symmetricus; or live Pacific sardine, Sardinops sagax. All hooks had a typical single barb on the point. Nearly all hooks had a gap distance from the point to the shank of 18-20 mm and were single hooks; however, some anglers occasionally used somewhat larger or smaller hooks or treble hooks.
[Figure 3 ILLUSTRATION OMITTED]
To enable identification of individual fish during the holding period, captured lingcod were tagged with model FD-94 numbered yellow anchor tags(2) anchored in the dorsal musculature between proximal pterygiophores. Fork length, sex (based on external genitalia), depth of capture, and terminal tackle (bait or lure) were recorded. Tackles with bait attached to a lure were recorded as bait.
Lingcod surviving immediate capture were placed in an onboard flow-through live well measuring 1.5 x 1.5 x 2 m. A habitat structure consisting of nine 102 mm diameter plastic pipes about 0.7 m long, bundled together, was placed in the live well to give the lingcod an opportunity to stabilize themselves within crevice-like locations and isolate themselves from one another. Lingcod in the live well were evaluated daily for condition and mortality and fed small live rockfish (Sebastes spp.) and other live baits to satiation in order to provide nutrition and discourage cannibalism.
On 29 September, 10 of the surviving lingcod and the habitat structure were transferred to Monterey Bay Aquarium where they were held in a 1.2 x 1.2 x 1.2 m continuous flow aquarium 18 days for further observation. Daily, they were evaluated and fed dead market squid to satiation.
Mendocino County
During January-August 1996, 69 lingcod were captured from Mendocino County waters (Fig. 3) from Department of Fish and Game vessels and chartered commercial fishing vessels. The lingcod were captured as part of a multipurpose nearshore reef fish tagging study. Again, sonar was employed to locate aggregations of fish over rocky habitats. Since a main purpose of the fishing was to capture rockfish for tagging and release with minimal injury, depths fished were usually less than 30 m, and bait was seldom used. Lingcod [is greater than] 61 cm total length were generally not retained because mortality to fish near or below the minimum size limit was of greatest interest. Rod and reel was the gear used on the multipurpose reef fish tagging trips. However, trolling gear was also used on two special trips targeting lingcod to evaluate mortality resulting from that gear and also to evaluate mortality of fish caught from depths [is greater than] 30 m.
The Mendocino County lingcod were tagged with dorsal anchor tags, like the Monterey County fish, or with 5 x 17 mm oval disk tags(2) attached to the opercular bone with fabric basting tacks.(3) Gear, depth of capture, hook location, fork length, and sex were recorded. The fish were held in onboard flow-through live wells and transported to the Fort Bragg High School Marine Laboratory at the end of the day. At the laboratory, the lingcod were segregated by size into different 1,0001 aquaria to minimize predation. Bundled plastic pipes were placed in the aquaria to provide habitat structure. Three times per week, the lingcod were observed and fed dead market squid or anchovy, Engraulis mordax, to satiation.
In both Monterey and Mendocino counties, the anglers (mainly Department of Fish and Game biologists or commercial fishermen) were instructed to handle the lingcod with the same care they would if they were recreational fishing. Some individuals wore rubber gloves to handle the fish, but most did not. The fish were not anesthetized for handling, so fish occasionally squirmed free and landed on the deck.
The holding period for fish that survived immediate hooking and landing ranged from 2-32 days ([bar] x= 15 days). At the end of the holding period, surviving lingcod were given a final examination and released to the ocean.
Results
Of the 84 lingcod captured, 65 were males, 17 were females, and the sex of two was not determined (Table 1). Fork length of males ranged from 355 to 686 mm; fork length of females ranged from 279 to 670 mm (Fig. 4). Capture depths ranged from 6 to 64 m.
Table 1.–Lingcod captured by hook and line gears and held for mortality observations.
Capture Fork
Fish Capture Capture Terminal depth length
no. date gear tackle (m) (mm)
1 9/24/95 Rod & reel Bait 18 508
2 9/24/95 Rod & reel Lure 27 503
3 9/24/95 Rod & reel Bait 23 602
4 9/25/95 Rod & reel Bait 37 598
5 9/25/95 Rod & reel Lure 37 416
6 9/26/95 Rod & reel Lure 20 521
7 9/26/95 Rod & reel Lure 27 337
8 9/26/95 Rod & reel Bait 27 453
9 9/26/95 Rod & reel Lure 9 670
10 9/27/95 Rod & reel Bait 27 435
11 9/27/95 Rod & reel Bait 23 630
12 9/27/95 Rod & reel Lure 21 600
13 9/28/95 Rod & reel Bait 23 568
14 9/28/95 Rod & reel Bait 23 572
15 9/28/95 Rod & reel Lure 47 603
16 1/11/96 Rod & reel Lure 14 462
17 1/11/96 Rod & reel Lure 14 490
18 1/11/96 Rod & reel Lure 14 446
19 1/11/96 Rod & reel Lure 14 544
20 1/11/96 Rod & reel Lure 14 686
21 3/1/96 Rod & reel Lure 13 597
22 3/1/96 Rod & reel Lure 13 609
23 3/1/96 Rod & reel Lure 13 430
24 3/1/96 Rod & reel Lure 13 509
25 3/1/96 Rod & reel Lure 13 636
26 4/5/96 Rod & reel Lure 13 345
27 4/5/96 Rod & reel Lure 13 428
28 5/6/96 Rod & reel Lure 27 383
29 5/6/96 Rod & reel Lure 27 355
30 5/6/96 Rod & reel Lure 27 372
31 5/6/96 Rod & reel Lure 27 367
32 5/6/96 Rod & reel Lure 27 378
33 5/6/96 Rod & reel Lure 27 365
34 5/6/96 Rod & reel Lure 27 357
35 5/6/96 Rod & reel Lure 27 514
36 5/6/96 Rod & reel Lure 27 447
37 5/6/96 Rod & reel Lure 27 530
38 6/27/96 Rod & reel Lure 7 498
39 6/27/96 Rod & reel Lure 7 375
40 6/27/96 Rod & reel Lure 8 464
41 6/24/96 Rod & reel Lure 10 484
42 6/24/96 Rod & reel Lure 10 488
43 6/19/96 Rod & reel Lure 6 627
44 6/20/96 Rod & reel Lure 20 378
45 6/20/96 Rod & reel Lure 20 455
46 6/19/96 Rod & reel Lure 6 549
47 6/19/96 Rod & reel Lure 6 543
48 6/27/96 Rod & reel Lure 7 568
49 6/19/96 Rod & reel Lure 6 545
50 8/5/96 Rod & reel Lure 18 408
51 8/5/96 Rod & reel Lure 16 481
52 8/5/96 Rod & reel Lure 16 507
53 7/30/96 Rod & reel Lure 20 402
54 7/30/96 Rod & reel Lure 20 589
55 7/30/96 Rod & reel Lure 20 589
56 7/30/96 Rod & reel Lure 20 459
57 7/30/96 Rod & reel Lure 20 408
58 7/30/96 Rod & reel Lure 10 465
59 7/30/96 Rod & reel Lure 12 456
60 7/30/96 Rod & reel Lure 20 279
61 8/21/96 Bar troll Lure 40 538
62 8/22/96 Bar troll Lure 55 519
63 8/22/96 Bar troll Lure 55 568
64 8/22/96 Bar troll Lure 55 575
65 8/22/96 Bar troll Lure 55 570
66 8/22/96 Bar troll Lure 55 550
67 8/22/96 Bar troll Lure 55 459
68 8/22/96 Bar troll Lure 55 554
69 8/22/96 Bar troll Lure 55 567
70 8/22/96 Bar troll Lure 55 608
71 8/22/96 Bar troll Lure 55 595
72 8/22/96 Bar troll Lure 55 480
73 8/22/96 Bar troll Lure 55 549
74 8/21/96 Bar troll Lure 64 525
75 8/21/96 Bar troll Lure 40 540
76 8/14/96 Rod & reel Lure 15 378
77 9/19/96 Rod & reel Lure 26 556
78 9/25/96 Rod & reel Bait 9 588
79 9/27/96 Rod & reel Lure 13 519
80 9/27/96 Rod & reel Lure 13 611
81 9/27/96 Rod & reel Lure 13 639
82 9/27/96 Rod & reel Lure 13 397
83 9/27/96 Rod & reel Lure 13 400
84 9/27/96 Rod & reel Lure 13 333
Capture- Holding- Wounds
Fish Days observed
no. Sex held healing
1 M 6
2 M 23 Yes
3 M 6 Yes
4 F 22 Yes
5 M 22 Yes
6 M 21 No
7 0 X
8 21 Yes
9 F 21 No
10 M 20 No
11 M 3
12 M 20 Yes
13 M 2
14 M 19
15 F 19
16 M 18
17 M 18
18 F 18
19 M 18
20 M 18
21 M 27 No
22 M 27
23 M 27
24 M 27 Yes
25 M 27
26 F 20 No
27 M 20
28 M 15
29 M 15
30 M 15
31 M 15
32 M 15
33 M 15
34 M 15 Yes
35 M 15
36 M 15
37 M 15 Yes
38 M 4
39 M 4
40 M 4
41 M 7
42 M 7
43 M 12 X No
44 M 11 Yes
45 F 11
46 M 12
47 M 12
48 M 4 X
49 M 12
50 M 11
51 M 11 Yes
52 M 11
53 F 17
54 M 17
55 F 17
56 F 17
57 M 17
58 M 17
59 M 17
60 F 0 X
61 M 9 Yes
62 M 8 Yes
63 M 8 Yes
64 M 8 Yes
65 M 8 Yes
66 F 8 Yes
67 F 8 Yes
68 M 8 Yes
69 M 8 No
70 M 8 Yes
71 F 8 Yes
72 M 8 Yes
73 F 8 Yes
74 F 9 No
75 M 9 Yes
76 M 16 Yes
77 F 32
78 M 26
79 M 24
80 M 24
81 M 24 Yes
82 M 24
83 M 24 No
84 F 24
[Figure 4 ILLUSTRATION OMITTED]
Three fish died during the holding period (Table 1). Of those three, one died of causes clearly attributable to capture. That fish, number 7, suffered a puncture wound to the ventral aorta when it was hooked and bled to death on landing. Another fish, number 60, died while being transported to the Fort Bragg High School Marine Laboratory, and another, number 48, died while being transported back to the ocean for release.
Fish number 43 survived the holding period but was very lethargic on release. It had developed an infection in the eye region where it had been punctured by the hook when captured. We assume fish number 43 did not survive long following release, and we attribute its death to injuries sustained during capture.
The deaths of fish numbers 48 and 60 were not attributable to any apparent physical injuries, and were probably due to physiological stress from being handled. Since fish 48 died 4 days after its capture and was handled shortly before death, we do not attribute its death to handling stress incurred during capture. Fish 60 died about 6 h after it was captured. Handling stress from capture probably contributed to its death because stress-induced blood parameter changes in fish can remain at least 6 h (Novak(4)). At 279 mm fork length, it was the smallest lingcod captured in the study. We conclude that, of the 84 fish captured, capture-related injuries caused the death of three fish (numbers 7, 43, and 60); cause was generally not difficult to discern.
All three of the capture-related mortalities were captured with rod and reel gear. The mortality rate for rod and reel gear is therefore 3/69 = 4.3%. For the binomial mortality rate (p), the variance (v) can be computed as
v = pq/n,
where q = 1-p and n is the sample size (Sokal and Rohlf, 1969). Assuming a normal approximation to the binomial distribution, the 95% confidence interval for the rod and reel mortality rate is 0-9.3%. None of the 15 lingcod captured with troll gear died of capture-related injuries.
Discussion
Due to the low overall mortality rate relative to the sample size, it is not possible to statistically isolate the effects of capture depth, terminal tackle, fish length, and sex on mortality. Much larger sample sizes would be needed to study those factors.
The three fish that died due to capture-related injuries were taken from a range of depths (6, 20, and 27 m). Fish were brought up from depths as great as 64 m with no signs of barotrauma (e.g. gas bubbles in the eyes). Lingcod lack a swim bladder and apparently do not suffer adverse gas expansion effects.
Fork lengths of the three capture-related mortalities were 279, 337, and 627 mm, an indication that smaller lingcod might prove to be more sensitive to capture-related mortality given a larger sample size. We noted capture-related wounds, typically hook punctures in the mouth area, in 38 of the fish held. In 26 of the 38 we observed evidence of healing (e.g. cessation of bleeding, smaller wound diameter) during the holding period. Wounds observed not healing were typically tears in poorly vascularized membranous tissues around the mouth.
Conclusions
Lingcod generally tolerated capture and handling well despite decompression, handling with nets and bare hands, and occasionally being dropped on the deck. Delayed mortality did not prove to be of significant concern. These results support the reputation of lingcod as a relatively hardy species and the use of a minimum size limit as a management tool.
Acknowledgments
We thank the following individuals and organizations for their assistance. On the Monterey coast, skipper Mark Kibby and the crew of the RV Mako assisted in capturing and holding lingcod, along with Bob Hardy, Shawn Melton, Paul Reilly, Connie Smithberg, and Carrie Wilson. The Monterey Bay Aquarium provided holding tank space for extended observation of captured lingcod, and Dave Lindquist provided feeding and care. On the Mendocino coast, the Salmon Trollers Marketing Association, through a grant from the U.S. Department of Commerce Northwest Emergency Assistance Program (NEAP), captured lingcod. Holding aquaria were provided by the Fort Bragg High School Marine Laboratory with the support of Fred Rubin. Cat Talbot and Pamela Wright assisted in transporting, evaluating, and caring for captured lingcod. Peter Kalvass edited the manuscript. John Geibel and Phil Law provided statistical guidance. We also thank the anonymous peer reviewers of the manuscript for editorial and statistical guidance. Partial funding was provided by the Federal Aid in Sport Fish Restoration Act (California Project F-50-R).
(1) PFMC. 1996. Status of the Pacific coast ground-fish fishery through 1996 and recommended acceptable biological catches for 1997: stock assessment and fishery evaluation. Pac. Fish. Manage. Counc. 2130 S.W. Fifth Ave., Suite 224, Portland, OR 97201.
(2) Floy Tag and Manufacturing Inc., Seattle, Wash. Mention of trade names or commercial firms does not imply endorsement by the National Marine Fisheries Service, NOAA.
(3) Quiltak Inc., Flagstaff, Ariz.
(4) K. Novak, D.V.M. 1996. Fish veterinarian, 700 N. Franklin St., Fort Bragg, CA 95437. Personal commun.
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Douglas Albin and Konstantin A. Karpov are with the California Department of Fish and Game, 19160 South Harbor Drive, Fort Bragg, CA 95437.3
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