NOAA Technical Memorandum NMFS-AFSC-173
 

Product Recovery Rates 

for Bled Sablefish 

by 

M. F. Sigler, D. Falvey, C. R. Lunsford, K. Barkhau, and L. Behnken 

U.S. DEPARTMENT OF COMMERCE 

National Oceanic and Atmospheric Administration
 

National Marine Fisheries Service
 

Alaska Fisheries Science Center
 

June 2007 
NOAA Technical Memorandum NMFS 

The National Marine Fisheries Service's Alaska Fisheries Science Center 

uses the NOAA Technical Memorandum series to issue informal scientific and 

technical publications when complete formal review and editorial processing 

are not appropriate or feasible. Documents within this series reflect sound 

professional work and may be referenced in the formal scientific and technical 

literature. 

The NMFS-AFSC Technical Memorandum series of the Alaska Fisheries 

Science Center continues the NMFS-F/NWC series established in 1970 by the 

Northwest Fisheries Center. The NMFS-NWFSC series is currently used by 

the Northwest Fisheries Science Center. 

This document should be cited as follows: 

Sigler, M. F., D. Falvey, C. R. Lunsford, K. Barkhau, and L. Behnken. 

2007. Product recovery rates for bled sablefish. U.S. Dep. Commer., 

NOAA Tech. Memo. NMFS-AFSC-173, 14 p. 

Reference in this document to trade names does not imply endorsement by 

the National Marine Fisheries Service, NOAA. 
NOAA Technical Memorandum NMFS-AFSC-173
 

Product Recovery Rates 

for Bled Sablefish 

by 

M.F. Sigler1, D. Falvey2, C. R. Lunsford1, K. Barkhau2, and L. Behnken2 

1 Alaska Fisheries Science Center
 

Auke Bay Laboratories
 

17109 Lena Loop Road
 

Juneau, AK 99801
 

2 Alaska Longline Fishermen’s Association
 

403 Lincoln Street, Suite 237
 

Sitka, AK 99835
 

www.afsc.noaa.gov 

U.S. DEPARTMENT OF COMMERCE 

Carlos M. Gutierrez, Secretary 

National Oceanic and Atmospheric Administration 

Vice Admiral Conrad C. Lautenbacher, Jr., U.S. Navy (ret.), Under Secretary and Administrator 

National Marine Fisheries Service 

William T. Hogarth, Assistant Administrator for Fisheries 

June 2007 
This document is available to the public through: 

National Technical Information Service 

U.S. Department of Commerce 

5285 Port Royal Road 

Springfield, VA 22161 

www.ntis.gov 
Notice to Users of this Document 

This document is being made available in .PDF format for the convenience of users; however, the 

accuracy and correctness of the document can only be certified as was presented in the original hard 

copy format. 

iii 

ABSTRACT 

Accurate catch estimates are necessary for successful fishery management. Catch weights 

may be affected by fish bleeding; a practice fishermen use to ensure product quality. We 

conducted field experiments during July 2002 and July 2003 in the Gulf of Alaska to estimate the 

change in fish weight due to blood loss for sablefish. Fish weights were compared before and 

after bleeding. Sablefish lost more weight when bled without seawater than when immersed in 

flowing seawater. Sablefish lost more weight when carefully brought aboard than when gaffed 

aboard (bled without flowing seawater). Gaffed sablefish lost weight even when not intentionally 

bled because of blood loss at the gaff wound. The product recovery rate (PRR) currently applied 

by fishery managers to estimate catch weight for bled sablefish (2.0%) slightly overestimates 

“blood loss” for fish gaffed aboard (1.7%). The PRR applied by fishery managers for unbled 

sablefish (0.0%) underestimates “blood loss” for fish gaffed aboard (1.0%). Estimating the actual 

change in weight due to blood loss for a commercial fishing trip is difficult because it requires 

accounting for storage methods and handling practices. 

v 

CONTENTS 

ABSTRACT ................................................................. iii

INTRODUCTION ............................................................. 1

MATERIALS AND METHODS .................................................. 2

RESULTS ................................................................... 4

DISCUSSION ................................................................ 5

Weight Measurements .................................................... 5

Accuracy of Currently Applied PRR ......................................... 6

Ability to Measure and Apply an Accurate PRR ................................ 7

ACKNOWLEDGMENTS ....................................................... 7

CITATIONS .................................................................. 9

TABLE ..................................................................... 11

FIGURES ................................................................... 12

INTRODUCTION 

Some fishermen bleed sablefish (Anoplopoma fimbria) to ensure product quality. Fish are 

bled by breaking or cutting gill rakers, then allowing the fish to bleed. The amount of blood lost 

likely is affected by several factors, some under the fishermen’s control and others not. Storage 

methods (ice or refrigerated seawater) and handling practices (gaffing, hook removal devices, 

and soak time) affect blood loss. 

The National Marine Fisheries Service (NMFS) applies a product recovery rate (PRR) for 

round, bled sablefish of 0.98 (NMFS product code 03) (Low et al. 1989). The PRR is used to 

estimate the live weight of landed bled sablefish by dividing the landed weight by 0.98. The 

current PRR dates back to the early 1980s and it is not known whether the figure was verified for 

sablefish1. The PRR is important to fishery managers for tracking fishery removals and to fishery 

scientists for assessing stock status. For example, average reported longline catch during 1999­

2003 was 12,942 t; an absolute error of 0.01 in the PRR would result in a catch estimation error 

of 129 t. The PRR also is important to fishermen because it affects the amount subtracted from 

the fishermen’s individual quota with each delivery of bled sablefish. For example, the effect of 

the 0.98 PRR is that for every 10,000 kg of bled sablefish delivered, 10,200 kg is deducted from 

that fisherman’s individual quota. 

Estimating an accurate PRR is challenging because several variables need testing. An 

experiment designed to estimate the actual PRR for sablefish would need to address storage 

methods and handling practices. Our approach was to estimate the change in weight due to blood 

1 Galen Tromble, Fishery Management Biologist, NMFS Alaska Regional Office, P. O. 

Box 21668, Juneau, AK 99801. Pers. commun., May 2002. 
2

loss expected for four treatments under controlled conditions. This approach both reduced the 

number of treatments and fit the length of field time available for this experiment. The study was 

a cooperative project between the Alaska Longline Fishermen’s Association and the NMFS Auke 

Bay Laboratory. The data were collected during the 2002 and 2003 NMFS sablefish longline 

surveys. 

MATERIALS AND METHODS 

The experiments were conducted on 25-26 July 2002 and 25-26 July 2003, on the upper 

continental slope near Yakutat Bay in the Gulf of Alaska. The chartered U.S. longline vessels, 

the F/V Alaskan Leader (overall length of 46 m) in 2002 and the F/V Ocean Prowler (overall 

length of 47 m) in 2003, deployed baited longline gear. Size 13/0 Mustad circle hooks were hand 

baited with chopped squid (Illex spp.). Three sets of 2,672 hooks each were deployed each day 

for a total of 6 sets during the 2-day experiment. Setting started at 0630 hours and retrieval 

started at 0930 hours. Soak time ranged from 3 to 8 hours. 

In 2002, fish were carefully released from the hook, dropped into a net, and then brought 

aboard the vessel to obtain an initial live weight. Only active fish in good condition were chosen. 

Fish were weighed before bleeding in a closed plastic pipe to still the fish. Fish were weighed 

with a Marel M1100 motion compensated marine scale. Scale accuracy was ± 2.5 g. The scale 

was calibrated at the beginning of each set retrieval. The closed plastic pipe was 15.2 cm 

diameter and 45.7 cm long and constructed of PVC. Neoprene fabric covered one end. The pipe 

rested in a cradle during weighing. After weighing, fish were marked with a unique tag and the 
3

two most posterior gill rakers on the fish’s right side were cut. Two treatments were carried out 

to test how handling practices affect blood loss. In the first treatment, fish were placed in a tank 

filled with flowing seawater to bleed. In the second treatment, fish were placed in a tub without 

any water to bleed. Slime was wiped off fish in the latter sample before weighing post-bleeding. 

Fish in flowing seawater did not accumulate slime on their skin and were not wiped. Clotted 

blood in the gill rakers was left in place. 

In 2003, fish were gaffed aboard the vessel rather than carefully releasing them from the 

hook as in 2002. Gaffing is the normal method of bringing fish aboard during longline fishing. 

Only active fish in good condition (before gaffing) were chosen. Fish were weighed immediately 

after gaffing in the closed plastic pipe. After weighing, fish were marked with a unique tag. Two 

treatments were carried out to test how handling practices affect blood loss. In the first treatment, 

the two most posterior gill rakers on the fish’s right side were cut. In the second treatment, the 

gill rakers were not cut. Fish in both treatments were placed in a tub without seawater to bleed. 

Slime was wiped off fish before weighing post-bleeding. Clotted blood in the gill rakers was left 

in place. The experimental treatments during 2002 and 2003 are summarized in Figure 1. 

Sampled sablefish were chosen by chance. After weighing one fish, the next fish retrieved 

from the longline was chosen for processing. This selection scheme resulted in sampling 

approximately one in every twelve fish. The ratio of the post-bleeding and live weight was 

computed for each sampled sablefish. For example, if the live weight was 3.5 kg and the postbleeding weight was 3.45 kg, then the ratio is 0.986. The distributions of ratios for sablefish bled 

without flowing seawater were skewed and not normal. The transformations of log, square root, 

reciprocal, and arcsine-square root did not change the distributions from skewed to normal. The 
4

median may be preferred to the mean for expressing central tendency for skewed populations and 

therefore, the median ratio was computed for each treatment and a confidence interval for the 

median was estimated (Zar 1984). The bootstrap method (Efron and Tibshirani 1986) also was 

applied to estimate the confidence interval and gave similar results to the method described in 

Zar (1984). 

RESULTS 

The total sample size was 611 sablefish (Table 1). Sample size by treatment ranged from 

74 to 252 fish. Average fish size was 3.7 kg round weight (Figure 2). Sablefish bled in flowing 

seawater frequently gained weight (Figure 3A), whereas all but one sablefish bled without 

seawater weighed less after bleeding (Figures 3B-D). For sablefish carefully brought aboard and 

with gills cut, the median ratio was 0.984 for sablefish bled in flowing seawater and 0.980 for 

sablefish bled without seawater (Table 1). These medians imply that blood loss typically is 1.6% 

for sablefish bled in flowing seawater and 2% for sablefish bled without seawater. For sablefish 

gaffed aboard and bled without flowing seawater, the median ratio was 0.983 for sablefish with 

gills cut and 0.990 for sablefish with gills left intact. These medians imply that blood loss 

typically is 1.7% for gills cut and 1.0% for gills left intact. 
5 

DISCUSSION 

Weight Measurements 

The change in weight due to blood loss was measured precisely. The 95% confidence 

intervals for the medians were narrow. For example the interval was 0.982–0.985 for sablefish 

bled in flowing seawater, a range of only 0.003. The range of confidence intervals was narrow for 

all treatments, only 0.003-0.007. 

Sablefish lost more weight when bled without seawater (2.0%) than with flowing 

seawater (1.6%) (gills cut, fish carefully brought aboard). The hydrostatic pressure of the water in 

the bleeding tank may act on the severed blood vessels to reduce blood volume loss. 

Alternatively, the heart, which continues to pump after the gill rakers are cut, may siphon 

seawater into the fish’s circulatory system, replacing the blood with seawater and possibly 

increasing circulatory system fluid volume. Finally, some water may have remained in the 

stomach of fish bled in flowing seawater, even though efforts were made to evacuate all water 

from the stomach prior to the post-bleeding weighing. 

Sablefish lost more weight when carefully brought aboard (2.0%) than when gaffed 

aboard (1.7%) (gills cut, bled without flowing seawater). Fishermen gaff the fish’s head, usually 

stunning the fish. Blood loss is reduced, probably because of the blow. Sablefish lost weight even 

when not intentionally bled (1.0%), probably because of blood loss at the gaff wound (gills left 

intact, bled without flowing seawater). 
6 

Accuracy of Currently Applied PRR 

The product recovery rate (PRR) currently applied by fishery managers to estimate catch 

weight for bled sablefish slightly overestimates blood loss for fish gaffed aboard. The National 

Marine Fisheries Service applies an adjustment to landings of bled sablefish that implies blood 

loss is 2% of body weight (PRR = 0.98, bled fish, product code 03). Gaffing fish is the normal 

method of bringing fish aboard during longline fishing. We found that blood loss is slightly less, 

1.7% of body weight for bled sablefish that are gaffed aboard. The implied PRR is 0.983 rather 

than the current 0.98. 

The PRR applied by fishery managers for unbled sablefish underestimates blood loss for 

fish gaffed aboard. No adjustment currently is applied for sablefish not deliberately bled (PRR = 

1.0, whole fish, product code 01) (Low et al. 1989); however, we found that blood loss is 1.0% of 

body weight for sablefish that are gaffed aboard. The implied PRR is 0.99 rather than the current 

1.0. 

Historical catch estimates represent the weight of sablefish after gaffing, rather than live 

weight. Most sablefish were gaffed aboard, classified as whole fish, and the PRR of 1.0 was 

applied. Historical catches underestimate the live weight of the catch by 1% because the correct 

PRR is 0.99. Fishery catches as well as catches from sablefish longline surveys are affected. For 

example, average reported longline catch during 1999-2003 was 12,942 t; estimated live weight 

is 13,073 t (=12,942 × 1.0 / 0.99). Thus the live weight of the catch was underestimated by 131 t. 
7 

Ability to Measure and Apply an Accurate PRR 

Common handling practices and storage methods affect blood loss. On sets left to soak 

overnight, a common practice in the fishery, some fish are dead, some are in poor condition, and 

some are active. Blood loss from fish retrieved dead or in poor condition, although not measured, 

likely is negligible and would reduce average blood loss accordingly. Conversely, we found fish 

bled in flowing seawater frequently gained weight. Therefore, blood loss may be different for fish 

stored in refrigerated seawater compared to fish stored on ice. 

Measuring and applying an accurate PRR is difficult given the variety of conditions 

existing in the fishery. Measuring an accurate PRR requires further studies of the effects of 

storage methods (ice or refrigerated seawater) and handling practices (gaffing, hook removal 

devices, and soak time), which would be time-consuming to complete. Applying the results of 

these studies would be difficult because the storage methods and handling practices would need 

quantification for each trip (e.g. percentage of fish retrieved dead). Accurately accounting for 

these factors would be complex and difficult, especially because blood loss is low. 

ACKNOWLEDGEMENTS 

This research was funded in part by the National Cooperative Research Program. We 

thank Dave Ackley, Jerry Pella, Phil Rigby, and Andy Smoker for reviewing this paper. We 

thank Dave Clausen and Mitch Lorenz, who in addition to Chris Lunsford and Kent Barkhau, 

collected the blood loss data. 

9 

CITATIONS 

Efron, B., and R. Tibshirani. 1986. Bootstrap methods for standard errors, confidence intervals, 

and other measures of statistical accuracy. Statistical Science 1:54-75. 

Low, L.-L., J. E. Smoker, L. J. Watson, J. D. Berger, and M. W. Eklund. 1989. A review of 

product recovery rates for Alaska groundfish. U.S. Dep. Commer., NOAA Tech. Memo. 

NMFS F/NWC-175, 22 p. 

Zar, J. H. 1984. Biostatistical analysis. Prentice-Hall, Inc., Englewood Cliffs, New Jersey. 

11 

Table 1.-- Median blood loss (ratio of post-bleeding and live weights) and 95% confidence 

intervals for median by treatment. 

Treatment Median Lower 95% 

confidence 

interval 

Upper 95% 

confidence 

interval 

Sample 

size 

Carefully released from hook, gills cut, bled 

in flowing seawater 

0.984 0.982 0.985 252 

Carefully released from hook, gills cut, bled 

without flowing seawater 

0.980 0.976 0.983 74 

Gaffed aboard, gills cut, bled in tub without 

flowing seawater 

0.983 0.981 0.985 128 

Gaffed, gills left intact, bled in tub without 

flowing seawater 

0.990 0.988 0.991 157 
12 

Figure 1. -- Flow diagram of experimental treatments. 

Bleed fish 

in flowing 

seawater 

Bleed fish 

in tub 

without 

seawater 

Bleed fish 

in tub 

without 

seawater 

Bleed fish 

in tub 

without 

seawater 

Carefully 

release fish 

from hook 

Cut gill 

rakers 

Cut gill 

rakers 

Leave gill 

rakers 

intact 

Gaff fish 

aboard 
13 

Figure 2.--Size distribution (live weight in kilograms, rounded to the nearest kilogram) of 

sablefish sampled in the bleeding study. 

300 

1 2 3 4 5 6 7 8 9 

Initial weight (kg) 

Frequency 

200 

100 

0 
14

Figure 3.--Frequency distributions of post-bleeding weight to live weight of sablefish bled 

without flowing seawater. A. Carefully released from hook, gills cut, bled in flowing 

seawater. B. Carefully released from hook, gills cut, bled in tub without seawater. C. 

Gaffed aboard, gills cut, bled in tub without seawater. D. Gaffed aboard, gills left 

intact, bled in tub without seawater. 

A 

0.8875 0.9025 0.9175 0.9325 0.9475 0.9625 0.9775 0.9925 1.0075 1.0225

Ratio of post-bleeding and live weights

B 

50

40

30

20

10

0

0.8875 0.9025 0.9175 0.9325 0.9475 0.9625 0.9775 0.9925 1.0075 1.0225

Ratio of post-bleeding and live weights 

0.8875 0.9025 0.9175 0.9325 0.9475 0.9625 0.9775 0.9925 1.0075 1.0225

Ratio of post-bleeding and live weights

D 

0.8875 0.9025 0.9175 0.9325 0.9475 0.9625 0.9775 0.9925 1.0075 1.0225

Ratio of post-bleeding and live weights

0 

10 

20 

30 

40 

50 

Frequency Frequency 

0 

10 

20 

30 

40 

50 

Frequency 

0 

10 

20 

30 

40 

50 

Frequency 

C 
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