Download Ichthyoplankton Collected on the 2004 and 2009

Ichthyoplankton Collected on the 2004 and 2009
Russian-American Long-Term Census of the Arctic Research Cruises
Morgan S. Busby1, Brenda L. Norcross2, Brenda A. Holladay2, and Kathryn L. Mier1
Alaska Fisheries Science Center, NMFS, NOAA • Seattle, WA USA
School of Fisheries and Ocean Sciences, University of Alaska Fairbanks • Fairbanks, AK USA
1
2
Arctic cod (Boreogadus saida) 56 mm SL
Introduction
The Russian-American Long-Term Census of the Arctic (RUSALCA) is an interdisciplinary joint
research effort conducted in U.S. and Russian territorial waters in the Bering Strait and Chukchi Sea.
Goals of RUSALCA include making physical, chemical, and ecological observations, understanding
impacts of climate variability in the Arctic ecosystem, and improving international Arctic science
collaboration. Research cruises were conducted in 2004, 2009, and 2012. Here we present results on
the taxonomic diversity of ichthyoplankton and the abundance, distribution, and lengths of Arctic
cod (Boreogadus saida) larvae and juveniles sampled during the 2009 survey and make comparisons
with the 2004 survey.
Methods
R/V Professor Khromov, Chukchi Sea, September 2009
Cruises were conducted aboard the Russian R/V Professor Khromov. Ichthyoplankton samples were
collected with a 60-cm bongo (0.505-mm mesh) in the Chukchi Sea at 18 stations 10–22 August 2004
and 31 stations 4–29 September 2009 (Figure 1a). Preserved samples were sorted and fishes
identified to the lowest taxonomic level possible at the Plankton Sorting and Identification Center in
Szczecin, Poland. Identifications were verified at the Alaska Fisheries Science Center (AFSC). Some
fish were categorized into taxonomic groups (e.g., Liparis spp.) due to limitations associated with
identifying larval stages to the species level. Fish were measured for standard length (SL) to the
nearest 0.1 mm. Abundance was estimated by converting number of individuals caught to
catch-per-unit-effort (CPUE) = # individuals/10 m2 sea surface area.
Results
Thirty-five larval and juvenile fishes were collected (11 species in 7 families) in 2009 (Table 1). Arctic
cod was the dominant species and accounted for 46% of the larvae and juvenile fishes caught.
Abundance and taxonomic diversity in 2009 were lower than in the 2004 RUSALCA survey that used
the same gear at fewer stations in a smaller geographic area. At the 13 stations sampled in both
surveys (Figure 1a), no Arctic cod were collected in 2009 while 101 individuals were caught at 8
stations in 2004 (Figure 1b). Shannon diversity was significantly greater in 2004 than 2009. (p=0.03)
(Table 2). Mean standard length of Arctic cod caught in 2009 was significantly greater than those
caught at all stations in 2004 (p<0.001) (Figure 2, Table 2). The CPUE of Arctic cod over all stations was
significantly greater in 2004 than in 2009 (p=0.002) (Table 2, Figure 1b).
Table 1. Fish eggs, larvae, and juveniles collected in 60-cm bongo tows in 2004 and 2009. Bold indicates families
(and/or taxa) present in both years.
Scientific Name
Common Name
2004 (n=18 stations)
Eggs
Larvae Juveniles
unidentified
Osmeridae
2009 (n=31 stations)
Eggs
Larvae Juveniles
Arctic cod
Eleginus gracilis
saffron cod
3
301
4
6
10
1
3
Theragra chalcogramma
walleye pollock
whitespotted greenling
Cottidae
Gymnocanthus spp.
unidentified Gymnocanthus
2
Gymnocanthus tricuspis
Arctic staghorn sculpin
2
Hemilepidotus papilio
butterfly sculpin
1
Icelus spatula
spatulate sculpin
3
Stichaeidae
Ammodytidae
3
50
1
Icelus spp.
unidentified Icelus
1
alligatorfish
3
Ulcina olrikii
Arctic alligatorfish
1
Liparis spp.
unidentified Liparis
20
Liparis fabricii
gelatinous seasnail
13
Liparis gibbus
variegated snailfish
36
Liparis tunicatus
kelp snailfish
1
Lumpenus spp.
unidentified Lumpenus
7
Lumpenus fabricii
slender eelblenny
4
1
Lumpenus maculatus
daubed shanny
3
1
Stichaeus punctatus
Arctic shanny
3
Ammodytes hexapterus
Pacific sandlance
45
40
1
35
30
3
unidentified flatfish
4
3
14
Hippoglossus stenolepis
Pacific halibut
Hippoglossoides robustus
Bering flounder
87
Limanda spp.
unidentified Limanda
17
Limanda aspera
yellowfin sole
67
Limanda proboscidea
longhead dab
1
Pleuronectes quadrituberculatus
2
3
4
23
3
1
11
2
111
498
6
47
22
13
Table 2. Results of statistical analyses.
2004
2009
Mean diversity index
0.89 ± 0.15
0.32 ± 0.20
Shannon, 2-sample t-Test
Mean Arctic cod length
16.3 ± 0.7
28.6 ± 1.9
2-sample t-Test
Median Arctic cod CPUE
2004
2009
20
15
5
0
8/
11
/0
8/ 4
12 B
/0 S
8/ 4 2
12 C
8 / /04 S 4
13
/0 CS
4
8
8/
14 CS
1
/0
8/ 4 2
15 C
8 / /04 L 3
16
/0 CL
4
6
8/
16 CL
1
/
0
0
8/
18 4
C
/
8 / 04 L 8
21
N
/0 o n
e
8/ 4
21 HC
/
3
0
9/
4
5
07
/0 No
ne
9
9/
C
08 E N
/
9 / 09 5
10
L
/0 S
9/ 9 3
22 S
S
/
9 / 09 4
23 S
S
/0
9 4
C
S
8
total number of individuals
25
10
3
Alaska plaice
total number of taxa
Metric
Our continuing work will focus on ichthyoplankton collected using bongo gear on the 2012 RUSALCA expedition.
1
Aspidophoroides monopterygius
Pleuronectidae
60-cm bongo gear
1
Hexagrammos stelleri
Liparidae
A 5.3 m2 mouth opening Methot net with 2x3-mm oval mesh towed at 3.0-3.5 knots catches larger walleye pollock than a 60-cm bongo net (0.283 m2
mouth opening) with 0.505-mm mesh (Bailey and Shima 1994). Thus, we suggest that a Methot, or similar net may be more effective at catching larger
larval and juvenile fish during late summer (September). In addition to the RUSALCA cruises, a 60-cm bongo with 0.505-mm mesh net was used to
collect ichthyoplankton during other recent surveys of the Chukchi (2007, 2008, 2012) and Beaufort (2008) Seas, and we recommend continuing to use
this gear as a consistent measure of CPUE for a long-term time series. Although survey continuity is highly desirable, we recognize it is not always
possible. To successfully assess species presence and size range of fish larvae, we recommend that future late summer surveys should sample
ichthyoplankton not only with bongo gear, but also with a Methot or similar net.
6
Hexagrammidae
Agonidae
Distinct ichthyoplankton species assemblages observed during the 2004 cruise were associated with different water masses (Norcross et al. 2010). Too
few larval and juvenile fishes were caught during 2009 to make definitive statements regarding summer ichthyoplankton assemblages in the Chukchi Sea.
1
unidentified cods
Boreogadus saida
Conclusions
2
capelin
Gadidae
Taxonomic diversity and mean abundance of larval fishes were substantially higher in 2004 than in 2009. These values were likely higher in 2004
because the cruises were in different months (August versus September) and growth experienced by Arctic cod during the additional month allowed
these larger individuals to avoid the bongo net in 2009. The central tendency, or median CPUE of Arctic cod for 2009 was zero because they were absent
from 84% of the sampled stations (Table 2). Confounding factors may include oceanographic conditions, climate variability, and biotic influences such as
prey availability and predation. The absence of flatfish larvae in 2009 is most likely due to settlement as late stage larvae and transforming individuals of
the most common Arctic species, Bering flounder (Hippoglossoides robustus), yellowfin sole (Limanda aspera), and longhead dab (Limanda proboscidea),
were present in the 2004 samples collected in August (Table 1).
47
unidentified smelts
Mallotus villosus
Figure 1 b. Stations where Arctic cod larvae and/or juveniles were caught.
Discussion
Length (mm)
Family
Figure 1 a. Bongo stations on 2004 and 2009 RUSALCA cruises.
9.3
0.0
Analyses
Mann-Whitney U
Date/Station
p -value
0.03
<0.001
0.002
Figure 2. Boxplots of mean lengths of Arctic cod larvae and juveniles caught in bongo tows, 2004 and 2009.
References
Acknowledgements
Bailey, K.L. and Shima, M. (1994) Comparative analysis of ichthyoplankton sampling gear for early life
history stages of walleye pollock (Theragra chalcogramma). Fish. Oceanogr. 3: 50-59.
This research was sponsored by the Cooperative Institute for Alaska Research, (CIFAR) with funds
from NOAA cooperative agreement NA08OAR4320870. We thank the NOAA Arctic Research Office,
Alaska Fisheries Science Center, and the scientists, officers, and crew of the R/V Professor Khromov.
Norcross, B.L., Holladay, B.A., Busby, M.S. and Mier, K.L. (2010) Demersal and larval fish assemblages in
the Chukchi Sea. Deep-Sea Res. II. 57:57-70.
The recommendations and general content presented in this poster do not necessarily represent the views or official position of the Department of Commerce, the National Oceanic and Atmospheric Administration, or the National Marine Fisheries Service.
Methot net