POST-MORTEM LENGTH CHANGES IN SIX FLORIDA FISH SPECIES

POST-MORTEM LENGTH CHANGES IN SIX FLORIDA FISH SPECIES

POST-MORTEM LENGTH CHANGES IN SIX FLORIDA FISH SPECIES STORED ON ICE
Thomas C. Chesnes, Raymond E. Waldner, and Cecilia S. Krahforst
Palm Beach Atlantic University, West Palm Beach, Florida, USA
ACKNOWLEGMENTS

SUMMARY RESULTS

MATERIALS AND METHODS

The authors wish to thank M. Chesnes, M. Thomas, and B. VanDusen for
assistance in specimen collection. L. Gregg (Florida Fish and Wildlife
Conservation Commission) provided valuable assistance in obtaining
collecting permits. J. Swick, R. Rulifson, C. Montague, and three
anonymous reviewers provided invaluable comments. This study was
partially funded by a 2004 Quality Initiative Grant from Palm Beach Atlantic
University.

All specimens were collected
via hook and line sampling.
Fish were euthanized and
placed on ice.
For every 30 minutes for six
hours, the measurements
described below were taken. In
addition, humidity and
temperature inside the cooler
were documented.

Family Lutjanidae

Family Centropomidae

Family Sciaenidae

Family Carangidae

Florida Reg: Total Length 15-20 slot,
1 over 20

Florida Reg: Fork Length 11-20,
1 over 20

A
A

A

3

6
11

4

Measurements Taken:

7
8

2

Standard Length-

10

8

8

2
9

7

6

3

1
3

2

2

3
5

5

6

5

1

4

2

1

2

3

2

3

1

2

3

3

-2
B

5

2

4

5

2

3

2
2

6
11

0

6

6

6

6

7

3
4

4

Percent Change

6

2

2

0

-2

3

4

4

5

3

3
4

-4

6

5

5

Anterior most point of the head to
a line connecting the tips of the
caudal fin, with tail naturally
splayed

2

5

4

5

4

6

4

4

3

0
4

3

4

2

2

2
3

2

2

2

2

2

3

6

4

5

4

4

2

-2

5

8

4

10

2

2

0

1

0

0

0

1

0

0

5

6

6

6

6

7

7

6

6

3

4

5

6

0
-2

1

2

-4

10

9

8

11

-1

12

-6

12

12

30

60

90

1

2

12

10

12

1

2
2

1

1

1

1

1

B

-1
-2

30

60

90

120 150 180 210 240 270 300 330 360
Time (minutes)

Time (minutes)

3
1

2

2

4

5

3

2
4

2

4
2

3
2
1

1

1
0

0

0

0

0

8

7

7

7

1

1

7

7

1
0

0

0
-1

5

5

8

8

7

8

4

2

-2

No Fork to measure

-3

0

30

3
60

90 120 150 180 210 240 270 300 330 360
3

7

1

1

1

1

1

1

1

1

C
3

0

2
6

-2
5

0

30

60

7

6

6

6

8

7

8

7

8

4

Time (minutes)

2

2

1
3

2

1

1

0
-1

4
3

-2

90 120 150 180 210 240 270 300 330 360

1

4

2
1

-3
0

120 150 180 210 240 270 300 330 360

Acuminate caudal fin

10

2

-2

-8
0

2

2

-3

-32

-1

0

2

-2

4

0

1

0

1

2
2

C

2

6

2

1

-2
-3

6

4

-1

4

-1

-3
B 2

3

1

0
-1

C

C

2

2

5

-2

-8

Total Length-

3

-1

7

-6

6

1

6

5

5

2

21

2

6

2

1

3
4

Percent Change

4

6

3

4

6

-8

Anterior most point of head to the
fork of the caudal fin

5

5

4

0

-1

-6

Fork Length-

1

5

5

0

2

3

-4

B

5
2

3

2

6

3

0
1

-2

Anterior most point of the head to
the terminal end of the hypural plate

9

A

1

0

INTRODUCTION

If anglers knew how much, if any, change in length to expect following a fishs
capture and storage on ice, they could determine how large a fish would have to be
in order to adhere to minimum and maximum legal length limits. Similarly,
enforcement officers would be able to better assess whether an angler had
intentionally harvested a fish protected by law. However, few studies have focused
on length changes in fishes following their capture, and fewer still have involved
fishes native to Floridas waters. Several studies have investigated shrinkage in
fishes subjected to storage in preservatives (Shetter 1936, Parker 1963, Stobo
1972, Lockwood and Daly 1975, Yeh and Hodson 1975, Jones and Geen 1977,
Theilacker 1980), freezing (Halliday and Roscoe 1969, Jones and Geen 1977,
Treasurer 1990, Armstrong and Stewart 1997), without any means of preservation
or freezing (Morison et al. 2003), and storage on ice (Lux 1960, Halliday and
Roscoe 1969, Rice et al. 1989, Gordon 1994, Blackwell et al. 2003). Only Rice et
al. (1989) dealt with a common Florida marine fish: the spotted seatrout (Cynoscion
nebulosus). The purpose of this study is to determine if six species of Florida
marine fishes belonging to different families change length when stored on
ice following capture, and to quantify these changes in order to provide
useful information for anglers and regulatory agency officers.

Florida Pompano- Trachinotus carolinus

Florida Reg: Total Length 28-32 slot
(Atlantic) , 28-33 (Gulf/Monroe)

Florida Reg: Total Length 8 minimum

Representatives of six species of fishes belonging to the families Lutjanidae,
Centropomidae, Pomatomidae, Scombridae, Carangidae, and Sciaenidae were
stored on ice for six hours after being euthanized, in order to assess postmortem length changes. Standard length, fork length (where applicable), total
length using the relaxed caudal fin method, and rigor mortis were measured
immediately following deaths and at thirty minute intervals thereafter. Two
species, Lutjanus synagris (L.) and Centropomus undecimalis (Bloch), showed
an increase in mean total lengths during the first hour following death.
Centropomus undecimalis continued to increase in mean total length for the
duration of the study, while L. synagris subsequently decreased. Declines in
mean standard, fork, and total lengths also were observed in Pomatomus
saltatrix (L.), Scomberomorus maculatus (Mitchill), and Trachinotus carolinus
(L.). Minimal changes in mean standard and total length were observed for
Cynoscion nebulosus (Cuvier). There was little direct correlation between rigor
mortis and length variation for any of the studied species. The observed length
changes may have implications for both law enforcement personnel and
anglers.

Spotted Seatrout- Cynoscion nebulosus

Percent Change

ABSTRACT

Lane Snapper- Lutjanus synagris

Snook- Centropomus undecimalis

Percent Change

This paper has been accepted for publication by the North American
Journal of Fisheries Management.

In the State of Florida the harvest of nearly all popular game and food fishes is
governed by regulations designed to prevent overexploitation. Regulations include
marine protected areas, closed seasons, bag limits, gear restrictions, and length
limits that vary from one species to another and, in some cases, between areas.
One potential problem may occur when fishes that just meet minimum length limits
at the time of capture may shrink to below the minimum legal length by the time
they are later measured by law enforcement officers. Fishes regulated by minimum
and maximum length (or slot) limits may also pose a problem if they expand
beyond the maximum allowable length. Thus, changes in fish length following
harvest may result in costly fines and the incarceration of anglers who
adhered to the regulations at the time the fishes were captured.

Figure Legend: Percent changes in mean standard (A), fork (B) and total (C) lengths of specimens over a six-hour period. Error
bars represent range; trend line is a linear regression. Numbers of fish increasing and decreasing in length from the baseline
measurement at each time interval are given above and below the baseline, respectively. In the interest of space, results for
Scomberomorus maculatus and Pomatomus saltatrix are not presented.

4

6
6

5

6

6

5

4

4

4

-3
0

30

60

90

120 150 180 210 240 270 300 330 360
Time (minutes)

Measurement of Rigor: Modified Cuttingss Method
These measurements were taken to determine if a relationship exists
between rigor mortis and changes in standard length.

In summary, after six hours:

In summary, after six hours:

Total Length In first hr , increase 2%,
after 6 hrs. decreases
average 3 %

Total Length increases average 1.5%

In summary, after six hours:
Total Length very little change

In summary, after six hours:
Fork Length - decreases average 1%

DISCUSSION

L. synagris (Lane Snapper) and C. undecimalis (Common Snook) potentially have the greatest effect on fishery management and enforcement due to the magnitude of
the changes observed in these species. Changes in mean standard and fork length measurements for both species were similar in slope and magnitude, but mean total length
using relaxed caudal fins - the measurement formerly used by Florida law enforcement officials for members of both Lutjanidae and Centropomidae - showed the greatest amount of
change over the six-hour measurement period.
A lesser degree of change in mean total length was seen in the species with less flexible caudal fins; i.e., S. maculatus (Spanish mackerel) and T. carolinus. (Pompano) The
linear regression slope and magnitude of length change over time was minimal for these species. In Florida, length limits of these species are determined by a fork length
measurement. Pomatomus saltatrix (Bluefish) is also regulated by fork length measurements in Florida and, like the above-mentioned species, only showed slight shrinkage in mean
fork length during the study period.

The change in mean total length of Cy. nebulosus (spotted seatrout) was extremely small (0.5%). These findings are consistent with the study Rice et al. (1989)
conducted in Texas, which documented a decrease in mean total length of 0.8% in this species.
Changes in length of fishes have been attributed in part to the onset of rigor mortis (Natsume 1995), although this was neither strongly supported in the present
study nor by Morison (2004).

Percent of individuals in full rigor at beginning of each measuring interval. Linear relationships between Rigor Index and
Standard Length. Statistically significant relationships are in bold.

0 30 60
Lutjanus synagris
Centropomus undecimalis
Pomatomus saltatrix
Scomberomorus maculatus
Trachinotus carolinus
Cynoscion nebulosus

Time (minutes)
90 120 150 180 210 240 270 300 330 360

0 8 8
8 17 25 33 75 83 83 92
0 0 38 50 63 75 75 75 75 75 75
0 29 43 43 57 57 57 57 86 86 100
0 11 22 44 66 66 78 89 100 100 100
0 13 75 100 100 100 100 100 100 100 100
0 0 0 11 78 100 100 100 100 100 100

92
75
100
100
100
100

92
75
100
100
100
100

Rigor and Standard Length
p
r2
0.0455
<0.01 0.0145 0.2239 0.1233 <0.001 0.1146 <0.001 0.0125 0.2593 0.014 0.2035 Increases in mean standard, fork, and total lengths were seen in the first hour of storage of L. synagris, (lane snapper) followed by a decrease in all measurements (Figure 1). Stobo (1972) noted this phenomenon in large yellow perch (P. flavescens (Mitchill)) stored in formalin, and suggested body relaxation as a possible cause. A loss of muscle tonus may also be responsible for the initial lengthening of some fishes in the present study. Desiccation may have played a major role in fish length changes. However, as neither weight nor water loss was measured in this study, we cannot state this for certain. Length changes were observed in most specimens in this study. Anglers who harvest regulated fishes of a length at or near the minimum (or in the case of C. undecimalis, maximum) limit could potentially, over time, be in possession of an illegal catch. A harvested individual of L. synagris initially measured at a length of 204 mm (8 in), slightly larger than the minimum limit, could shrink approximately six mm (0.24 in) if the length decreases at the average amount documented in this study. Likewise, an individual of C. undecimalis initially measured at 838 mm (33 in), slightly shorter than the maximum length allowed in Floridas Gulf waters, could lengthen by approximately 1 cm (0.39 in), if it lengthens at the average value measured. In both instances, the angler would be in possession of an illegal fish and could be subject to penalty. PBA Biology graduate Cecilia Krahforst (05) was funded by the Faculty Quality Initiative research grant. She is currently a doctoral candidate at East Carolina University. She is a coauthor of the peer reviewed paper of this study published in the North American Journal of Fisheries Management along with Drs. Waldner and Chesnes.

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