The influence of environmental factors on halibut distribution as ...

The influence of environmental factors on halibut distribution as observed on the IPHC stock assessment survey: A preliminary examination Lauri L. Sadorus

Abstract The International Pacific Halibut Commission (IPHC) began collecting oceanographic data opportunistically alongside survey catch data in 2000. In 2009, as a result of a significant grant, the IPHC launched a coastwide oceanographic data collection program. To date, 5,896 successful water column profiles have been collected. There is evidence that both dissolved oxygen and temperature play a role in halibut distribution within the survey area, and as environmental conditions change both spatially and temporally, understanding how distribution is affected is imperative to evaluating survey catchability throughout the halibut range.

Introduction Fishery science has evolved in recent years from simple single-species catch models to more elaborate ecosystem-based models that include an array of information. Fluctuating oceanographic conditions and longer term changes related to climatic shifts have dictated the need for a better understanding of environmental impacts on fish distribution and abundance. Modern oceanographic monitoring takes place in a variety of ways including free drifting gliders, moorings, and satellite imaging of the ocean surface. However, these methods do not integrate fishery catch data. Technological developments in recent years have enabled the collection of oceanographic information at depth in a more cost and time-effective manner, making it possible to collect these data alongside other data types such as species catch information. Environmental conditions in the north Pacific The north Pacific and Bering Sea are home to a complex system of ocean currents and a variety of environmental conditions affecting distribution and relative abundance of fish species. Climate change has begun to produce significant changes to many of these conditions and scientists are increasingly interested in describing both baselines and changes in oceanography and their effects on organisms. The following sections provide a brief background on the environmental variables of interest in the region and why their investigation is important to the International Pacific Halibut Commission (IPHC). Dissolved oxygen Dissolved oxygen (DO) is naturally low in deeper water that can be pushed up onto the continental shelf (less than ~500 m depth) during coastal upwelling events. Upwelling occurs off the U.S. West Coast in the spring and summer months and can also occur intermittently and in lower strengths throughout the survey region. Low DO can also develop in more shallow, nutrient-rich waters where primary production supply exceeds the zooplankton demand; as the excess phytoplankton dies and sinks, bacterial respiration depletes, the already poorly oxygenated 401 IPHC Report of Assessment and Research Activities 2012

deeper water of its remaining oxygen, resulting in a low or hypoxic condition (DO < 1.4 ml/L and considered toxic to animals). Hypoxia occurs naturally in coastal upwelling zones like the U.S. West Coast (Diaz and Rosenburg 2008) and has been regularly recorded further north, off southern British Columbia (B.C.) (Irvine and Crawford 2008). To date, the most notable hypoxic event recorded within the survey area and time frame occurred in 2006, where waters near Heceta Bank off Oregon became hypoxic in mid-June and persisted until mid-October. During this time, hypoxia deteriorated into anoxia (no oxygen) and persisted for several weeks, resulting in large kills of stationary and slow moving invertebrates and crustaceans (PISCO, retrieved October 13, 2011). Washington has experienced hypoxic conditions since the historical record began in the 1950s and experienced hypoxia outside of the historical boundaries in 2006 (Connolly et al. 2010). Bakun (1990) predicted that as CO2 and other greenhouse gas levels rise in the earth’s atmosphere, inhibited nighttime cooling and enhanced daytime heating would lead to intensified continental thermal lows. These intensified lows would cause increased onshore-offshore pressure gradients and intensified alongshore winds. Alongshore winds are responsible for coastal upwelling, so in this scenario, upwelling would ultimately be accelerated. Barth et al. (2007) examined the coastal upwelling off the Oregon coast in 2005. He found that the onset of seasonal upwelling was delayed well into the summer due to slack winds, but when the north winds did commence they lasted longer in each cycle and were stronger than average. This resulted in larger and more persistent plankton blooms, and eventually hypoxia. It is also theorized that due to rising global temperature and resultant increased stratification of the world’s oceans, the oxygen minimum zones (OMZs), which are the naturally cold, low DO water in the deep ocean basins, are expanding and bringing this water closer to the continental shelf, thus facilitating the annual recurrence of upwelling-induced hypoxia even in years of moderate upwelling winds (Keeling et al. 2010). Whitney and Freeland (1999) and Whitney et al. (2007) reported that water measurements taken at a station along the “P” line off Vancouver Island, B.C. (located at 50oN, 145oW) over a 50 year period (1949 – 1999), clearly show wide inter-annual variability and longer term shoaling of the hypoxic OMZ boundary. If Keeling et al.’s (2010) hypothesis is true, more hypoxic areas will emerge along continental shelf regions of low to moderate upwelling strength as the OMZs expand. Organisms have varying responses and tolerances to hypoxia. Generally, invertebrates and slow moving organisms are more vulnerable to seasonal hypoxia because they are unable to move to more oxygenated water (Rabalais et al. 2002). Mobile organisms show a variety of responses such as changes in swimming speed (Metcalfe and Butler 1984), reduced growth and metabolism (Gray et al. 2002), and changes in predatory behavior intensity (Pollock et al. 2007). Several studies showed that mobile organisms were able to move from low DO areas, but were displaced from their normal habitat, leading to increased vulnerability to predators, habitat compression, and overlap with species not normally encountered (Pihl et al. 1991, Gray et al. 2002, Diaz and Rosenberg 2008). Temperature Bottom temperature within the survey area varies from relatively warm waters in the south to very cold waters in the northern Bering Sea. Surface waters are warming globally, at a rate of about 0.2oC/decade, and the warming is expected to continue in, both the surface layer and deeper waters (U.S. EPA 2010). 402 IPHC Report of Assessment and Research Activities 2012

The effects of temperature changes on organisms appear to vary. For example, Hurst (2007) documented increased swimming speed and decreased schooling behavior with decreasing temperatures for juvenile walleye pollock. Perry et al. (2005) conducted a 25-year study of fishes in the North Sea and documented a northward contraction of distribution for several species as temperatures increased over time. Stoner et al. (2006) studied Pacific halibut in the laboratory and found altered feeding responses related to temperature changes. Salinity Salinity within the survey area is currently well within ranges seen in the coastal oceans. Generally speaking, fresher (lower salinity) water tends to be at the ocean surface where seawater mixes with rainfall or where freshwater inputs from rivers and estuaries are present. Worldwide, average ocean salinity ranges from 33-37 psu (NODC 2011) and there is seasonal variability with annually varying subsurface currents (Bingham et al. 2010). Over the long term, as increasing temperatures melt polar and glacial ice, which is fresh water, the surface ocean layer will have lower salinity. At Ocean Station ‘Papa’ off Vancouver Island, a 42-year time series of observations (1956-1997) shows a warming and freshening trend (Freeland et al. 1998). Salinity is important for organisms in the role that it plays in the stratification of ocean layers, i.e., stronger stratification will result in reduced ocean mixing and intensification of other changing conditions like DO and temperature. Acidity The world’s oceans act as a “sink” for CO2 that exists naturally in the atmosphere and have absorbed 30-40% of the anthropogenic CO2 from the industrial age, reducing the effects of global climate change (Feely et al. 2009). However, this absorption has come at a cost to the oceans in the form of ocean “acidification”, which refers to the decreased pH of the ocean caused by the chemical reaction of seawater and anthropogenic CO2 (Broecker and Clarke 2001). Anthropogenic CO2 has resulted in a reduction of oceanic pH by about 0.1. (Caldeira and Wickett, 2003, 2005; Orr et al. 2005) and is projected to cause pH to decrease another 0.3 units by the year 2100 (Friedlingstein et al. 2006). Marine calcifying organisms, such as various species of plankton, corals, and molluscs experience decreased ability to form shells as the pH of the seawater decreases (Doney et al. 2009). This has the significant potential to disrupt the food chain by reducing the amount and type of food available at lower trophic levels. A review of the literature by Fabry et al. (2008) reported that acidification resulted most often in metabolic suppression, affecting feeding, growth, and reproduction in fishes. Preliminary research presented by P. Munday (James Cook University, Township, Australia) at the 2012 Symposium on the Ocean in a High CO2 World, reported behavioral changes not only in prey species, but also in predatory fishes, resulting in changes to the type of prey consumed. The effect of pH levels on halibut biology is poorly known. This study provides the first comprehensive data collection for halibut habitats. Chlorophyll The measure of chlorophyll in the water column corresponds to the amount of primary production (phytoplankton) currently in the water. Chlorophyll production takes place near the surface in the photic zone (where light is penetrating the water layers) and increases with nutrient input from upwelling or terrestrial runoff. Plankton blooms can affect the DO chemistry of the 403 IPHC Report of Assessment and Research Activities 2012

water column, i.e., increasing the DO in the near-surface layer and reducing the DO below the photic zone. Phytoplankton is not consumed directly by halibut, but affects the overall productive environment where multiple trophic levels are present.

History of the IPHC profiler program Historically, oceanographic and catch data were collected separately because oceanographic data collection was very expensive and required specialized vessels and equipment. The development of a self-contained, high performing instrument that could be deployed from the deck of any vessel was the technological advance needed to pair these data. Seabird Electronics Inc., located in Bellevue, Washington developed such an instrument, and in 2000, the IPHC purchased one unit to be deployed on different vessels and in different areas over several years, as a proof of concept (Hare 2001). The project was a success, proving oceanographic data could be collected alongside catch data without a large time investment, using the same vessels and gear already employed for the setline survey. From 2000 to 2004, the profiler collected pressure (depth), temperature, and conductivity (salinity) data throughout the water column. In the 2000s, dissolved oxygen (DO) became a feature of interest in fisheries, as it was discovered that large areas of very low oxygen (called hypoxic zones) were expanding and growing in number worldwide (Diaz and Rosenburg 2008). In 2005, a DO sensor was added to the profiler to assess the level of oxygen experienced by the fishes encountered on the IPHC survey. In 2005, the profiler was dedicated to the southern B.C. areas to begin building a consistent time series. With the identification of several years of hypoxia off the U.S. West Coast and a particularly significant event off Oregon in 2006, scientists inside and outside the IPHC had increased interest in the geographic range and severity of these events and how they might be affecting fish distributions. Another oceanographic feature that began gaining particular interest in the 2000s was ocean acidification. In 2007, the IPHC received a grant from the Oregon Department of Fish and Wildlife Restoration and Enhancement Program to purchase a profiler dedicated to the survey stations off the Oregon coast. This second profiler (Seabird model SBE19plus) was purchased with the capability to measure all of the factors of the original profiler including DO, and additionally, pH and chlorophyll a concentration. In 2007, this profiler was deployed only at survey stations off Oregon and beginning in 2008, at survey stations off both Oregon and Washington. The IPHC conducts one of the most spatially comprehensive annual fishery surveys in the north Pacific. Commission stock assessment scientists advocated the coastwide collection of oceanographic data alongside catch data with the eventual goal of investigating environmentally related catchability issues. Outside the Commission, oceanographic scientists were interested in greater knowledge of the north Pacific continental shelf, an area largely unsampled by past programs. Therefore, in 2008, the IPHC received a significant grant from the National Oceanic and Atmospheric Administration (NOAA) to purchase and deploy 14 profiler units (Seabird model SBE19plusV2) on the coastwide IPHC setline survey. These units collected all of the same information as the unit purchased with the previous grant for Oregon and have been deployed since 2009, resulting in four consecutive years of coastwide data. Stipulated in the NOAA grant was that the data must be made available to scientists worldwide as soon as possible following collection. To that end, the IPHC contracted with the University of Washington Joint Institute for the Study of the Atmosphere and Ocean (JISAO) and the NOAA 404 IPHC Report of Assessment and Research Activities 2012

Pacific Marine Environmental Laboratory to process and post the data. As of the writing of this paper, oceanographic data for 2009-2011 have been completed and posted, and 2012 data are in progress. To date, a total of 5,896 profiles have been collected since 2000. Prior to 2005, the lone unit was deployed opportunistically. Since 2005, standardized protocols and areas were established for launching the unit(s). Table 1 shows the successful profiles for each survey region from 20002012.

Halibut NPUE and environmental factors The coastwide distribution of halibut has varied somewhat over the 2009-2011 time period as exploitation intensities have changed, but major patterns have remained similar from year to year (Fig. 1). In recent years, the survey has routinely seen the highest halibut numbers in the central and western Gulf with fewer numbers and/or higher variability among stations in the areas further south along the west coast and into the Bering Sea and Aleutian Islands. Near-bottom environmental conditions experienced during the summer survey from 2009 to 2011 are illustrated in the online version of Sadorus and Walker (2012). There have been fairly consistent water temperatures throughout the Gulf and colder water further north in the Bering Sea. Lower DO is a feature regularly found off the West Coast, in recent years. DO increases further north into the eastern Gulf but remains relatively low, then gives way to much higher DO levels to the west. Less obvious in the maps is the fact that deeper stations tend to have lower DO than more shallow stations, with the exception being the West Coast where upwelling induced hypoxia extends to nearshore areas. pH and chlorophyll tend to be highly variable both temporally and spatially. The area surveyed is known halibut habitat, so the expectation is to find environmental factors within the range tolerated by halibut. One way to see how halibut distribution may be affected as climate change forces environmental variables beyond these “normal” ranges, is to look at conditions on the fringes of the habitat. For example, the coasts of Washington and Oregon are at the southern geographic range of halibut habitat and this area experiences particularly low DO. In fact, plotting number per unit effort (NPUE) versus DO levels (Fig. 2) shows what appears to be, a minimum tolerance threshold for oxygen at about 0.9 ml/L. When looking at NPUE overlaid with DO for the West Coast, stations that experienced particularly low DO had very little or no halibut compared to stations with higher levels (Fig. 3). The difference in halibut NPUE related to DO is also evident when looking across years. The spatial extent of low DO varied by year. In 2009, hypoxic conditions were observed throughout the southern range from offshore to nearshore, and 2011 hypoxic conditions were less intense and mostly at the stations further offshore. While halibut presence may be affected by multiple factors, it is significant that in 2011, following two years of fairly intense hypoxia, halibut were caught at stations that were hypoxic in previous years and above the hypoxia threshold in 2011. This adds credibility to the theory that DO is a contributing factor to distributional changes for halibut. A similar examination can be conducted in the Bering Sea where low temperature may be a factor limiting fish distribution. Pacific halibut routinely occupy waters ranging in temperatures from about 2-8oC, though they have been known to occasionally occur outside of these ranges. In the Bering Sea, bottom temperatures below zero have been observed on the survey, at the most northerly stations. A scatterplot of NPUE versus temperature for 2009-2011 (Fig. 4) shows 405 IPHC Report of Assessment and Research Activities 2012

that there may be a minimum temperature threshold for halibut at around 0.5oC, since no halibut were caught at stations with temperatures below this. However, the number of stations (around St. Matthews Island) with very low temperatures was small, requiring more data on this effect (Fig. 5). Both these temperature and DO observations provide indication of potential effects on survey catch rates that can be incorporated into our understanding of results. Survey catchability is likely to be broadly related to current and future environmental conditions during the survey. The survey gear is passive, in that it depends on animal behavior to make it work. As discussed in the introduction, many studies have shown changes in animal behavior related to environmental conditions, e.g., changes in feeding patterns related to temperature, prey composition related to acidity, and habitat avoidance related to DO. All of these things could affect the catchability of the fishing gear during the survey. Sadorus (In prep) analyzed environmental factors in relation to survey halibut catch off the West Coast and found geographic non-stationarity, i.e., that the relationship between environmental factors and catch was not the same throughout the study area. It is unclear whether non-stationarity is a result of an environmental threshold being reached (in this case minimum DO tolerance) or whether it is a symptom across the halibut range. Examining data over more years and a larger area will help to verify the extent of the nonstationarity issue, and add to the IPHC’s knowledge of survey catchability for application in the IPHC stock assessment.

References Bakun, A. 1990. Global climate change and intensification of coastal ocean upwelling. Science 247: 198–201. Barth J. A., Menge, B. A., Lubchenco, J., Chan, F., Bane, J. M., Kirincich, A. R., McManus, M. A., Nielsen, K. J., Pierce, S. D., and Washburn, L. 2007. Delayed upwelling alters nearshore coastal ocean ecosystems in the northern California current. PNAS vol. 104, no. 10: 37193724. Bingham, F. M., Foltz, G. R., and McPhaden, M.J. 2010. Seasonal cycles of surface layer salinity in the Pacific Ocean. Ocean Sci., 6: 775–787. Broecker, W., and Clarke, E. 2001. A dramatic Atlantic dissolution event at the onset of the last glaciation. Geochemistry Geophysics Geosystems 2(11):1,065, doi:10.1029/2001GC000185. Caldeira, K., and Wickett, M.E. 2003. Anthropogenic carbon and ocean pH. Nature 425(6956):365. Caldeira, K., and Wickett, M.E. 2005. Ocean model predictions of chemistry changes from carbon dioxide emissions to the atmosphere and ocean. Journal of Geophysical Research 110, C09S04, doi:10.1029/2004JC002671. Connolly, T. P., Hickey, B. M., Geier, S. L., and Cochlan, W. P. 2010. Processes influencing seasonal hypoxia in the northern California Current System. J. Geophys Res. 115: 22 p. Diaz, R. J. and Rosenberg, R. 2008. Spreading Dead Zones and Consequences for Marine Ecosystems. Science. 15, Vol. 321: 926-929. Doney, S. C., Fabry, V. J., Feely, R. A., and Kleypas, J. A. 2009. Ocean Acidification: The Other CO2 Problem. Rev. Mar. Sci. 2009. 1:169–92. 406 IPHC Report of Assessment and Research Activities 2012

Fabry, V. J., Seibel, B. A., Feely, R. A., and Orr, J. C. 2008. Impacts of ocean acidification on marine fauna and ecosystem processes. – ICES Journal of Marine Science, 65: 414–432. Feely, R. A., Doney, S. C., and Cooley, S. R. 2009. Ocean acidification, present conditions and future changes in a high CO2 world. Oceanography, vol. 22, no. 4: 36-47. Freeland, H., Denman, K., Wong, C. S., Whitney, F., and Jacques, R. 1998. Evidence of change in the winter mixed layer in the northeast Pacific Ocean. Deep Sea Res. Vol. 44, No. 12: 2117-2129. Friedlingstein, P., Cox, P., Betts, R., Jones, C., von Bloh, W., Brovkin, V., Cadule, P., Doney, S., Eby, M., Fung, I., Bala, G., John, J., Jones, C., Joos, F., Kato, T., Kawamiya, M., Knorr, W., Lindsay, K., Matthews, H. D., Raddatz, T., Rayner, P., Reick, C., Roeckner, E., Schnitzler, K. G., Schnur, R., Strassmann, K., Weaver, A. J., Yoshikawa, C. and Zeng, N. 2006. Climate-carbon cycle feedback analysis: Results from the C4MIP model intercomparison. Journal of Climate 19(14):3337–3353. Gray, J. S., Wu, R. S., and Or, Y. Y. 2002. Effects of hypoxia and organic enrichment on the coastal marine environment. Mar. Ecol. Progress Series 238: 249-279. Hare, S. H. 2001. Deployment of a water column profiler from a halibut longliner during IPHC survey operations. Int. Pac. Halibut Comm. Report of Assessment and Research Activities 2000: 257-264. Hurst, T. P. 2007. Thermal effects on behavior of juvenile walleye Pollock (Theragra chalcogramma): implication for energetic and food web models. Can. J. Fish. Aquatic Sci. 64:449-457. Irvine, J. R. and Crawford, W.R. 2008. State of physical, biological, and selected fishery resources of Pacific Canadian marine ecosystems. Research paper [In] Canadian Science Advisory Secretariat. Fisheries and Oceans Canada. Keeling, R. F., Kortzinger, A. K., and Gruber, N. 2010. Ocean deoxygenation in a warming world. Annual Review of Marine Science Vol. 2: 199-229. Metcalfe, J. D. and Butler, P. J. 1983. Changes in activity and ventilation in response to hypoxia in unrestrained, unoperated dogfish (Scyliorhinua canicula L.) J. Exp. Biol. 108: 411-418. National Ocean Data Center (NODC). 2011. World Ocean Atlas 2009. Retrieved October 27, 2011. http://www.nodc.noaa.gov/OC5/WOA09/pr_woa09.html Orr, J.C., Fabry, V.J., Aumont, O., Bopp, L., Doney, S.C., Feely, R.A., Gnanadesikan, A., Gruber, N., Ishida, A., Joos, F., Key, R. M., Lindsay, K., Reimer, E. M., Matear, R., Monfray, P., Mouchet, A., Najjar, R. G., Plattner, G. K., Rodgers, K. B., Sabine, C. L., Sarmiento, J. L., Schlitzer, R., Slater, R. D., Totterdell, I. J., Weirig, M. F., Yamanaka, Y., and Yool, A. 2005. Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms. Nature 437(7059):681–686. Partnership for Interdisciplinary Studies of Coastal Oceans (PISCO). 2011. Frequently asked questions about hypoxia and the Pacific Northwest ‘Dead Zone’. Retrieved October 13, 2011 from http://piscoweb.org/hypoxia-faq#id3328697725. 407 IPHC Report of Assessment and Research Activities 2012

Perry, A. L., Low, P. J., Ellis, J. R., and Reynolds, J. D. 2005. Climate Change and Distribution Shifts in Marine Fishes. Science, Vol. 308:1912-1915. Pihl, L., Baden, S. P., and Diaz, R. J. 1991. Effects of periodic hypoxia on distribution of demersal fish and crustaceans. Mar. Biol. Vol. 108, No. 3: 349-360. Pollock, M. S., Clarke, L. M. J., and Dube’, M. G. 2007. The effects of hypoxia on fishes: from ecological relevance to physiological effects. Environ. Rev. 15: 1-14. Rabalais, N. N., Turner, R. E., and Wiseman, W. J. Jr. 2002. Gulf of Mexico Hypoxia, a.k.a. “The Dead Zone”. Annual Review of Ecology and Systematics, Vol. 33 (2002): pp. 235-263. Sadorus, L. L. In prep. Exploring the role of oceanographic features in the spatial distribution of Pacific halibut and other longline-caught fishes off the west coast from southern Oregon to Queen Charlotte Sound, British Columbia. MS thesis, University of Washington, School of Aquatic and Fishery Sciences, Seattle, WA. Sadorus, L. L. and Walker, J. 2012. Oceanographic monitoring during the IPHC setline survey in 2011. Int. Pac. Halibut Comm. Report of Assessment and Research Activities 2011: 413424. Online version of 2009-2011 maps: http://www.iphc.int/publications/rara/2011/2011. Appendix11.pdf Stoner, A. W., Ottmar, M. L., and Hurst, T. P. 2006. Temperature affects activity and feeding motivation in Pacific halibut: Implications for bait-dependent fishing. Fish. Res. 81: 202209. U.S. EPA. 2010. Climate change indicators in the United States. EPA 430–R–10–007. www.epa. gov/climatechange/science/indicators/. Whitney, F. A., and Freeland, H. J. 1999. Variability in upper-ocean water properties in the NE Pacific Ocean. Deep-Sea Research II 46: 2351-2370. Whitney, F. A., Freeland, H. J., and Robert, M. 2007. Persistently declining oxygen levels in the interior waters of the eastern subarctic Pacific. Progress in Oceanography 75: 179-199.

408 IPHC Report of Assessment and Research Activities 2012

409

IPHC Report of Assessment and Research Activities 2012

3B 4A 4A, 4C 4D 4B 4B

Sanak

Unalaska

4A Edge

4D Edge

Adak

Attu

Total

3B

Shumagin

3A

Seward

3B

3A

Prince William Sound

Chignik

3A

Yakutat

3B

3A

Fairweather

Semidi

2C

Sitka

3B

2C

Ommaney

Trinity

2C

Ketchikan

3A

2B

Charlotte

Albatross

2B

St. James

3A

2B

Goose Island

Shelikof

2B

Vancouver

3A

2A

Puget Sound

Portlock

2A

Washington

3A

2A

Oregon

Gore Point

Area

IPHC survey region

142

51

49

42

2000

119

20

4

45

21

29

2001

25

25

2002

275

41

48

36

36

41

38

35

2003

14

2

12

2004

116

4

38

36

38

2005

149

36

41

38

34

2006

Year

168

40

37

35

15

41

2007

222

38

39

24

40

40

41

2008

1,245

40

43

68

57

64

48

43

44

47

47

33

45

46

43

44

45

51

49

42

40

38

42

41

43

41

59

42

2009

1,138

44

44

57

56

51

28

0

42

41

44

44

38

43

45

48

45

51

48

42

39

37

41

42

43

41

42

42

2010

1,193

41

25

63

42

61

48

35

47

40

46

44

44

45

44

46

45

48

29

42

37

41

42

37

40

37

14

57

53

2011

1,090

44

42

44

33

56

38

16

42

47

47

45

42

27

45

48

45

48

45

39

39

22

38

38

42

41

46

31

2012

Table 1. Oceanographic profiles collected by IPHC during the summer stock assesment survey by year and area. Prior to 2005, profiles were collected opportunistically. In 2005, “core” areas were designated and by 2009, standardized protocols were adopted coastwide.

2011

2010

2009

Figure 1. NPUE of Pacific halibut during the standardized setline survey, 2009-2011. 410 IPHC Report of Assessment and Research Activities 2012

411


0

5

10

15

20

25

30

35

0

1

DO=0.9 ml/L

2

3 DO (ml/L)

4

5

Area 2A and southern 2B: 2005‐2011

6

7

Figure 2. A scatterplot of near bottom dissolved oxygen (DO) versus halibut NPUE for the U.S. West Coast and southern B.C. coast regions of the survey, 2005-2011. An apparent minimum DO tolerance threshold is indicated at 0.9 ml/L.

Halibut NPUE

412


2010

2011

Figure 3. Survey SurveyNPUE NPUE halibut overlaid on an isosurface map DO of near bottom for each 2009-2011, for the coasts ofand Oregon, Figure 3. ofof halibut overlaid an isosurface map of bottom for each year, DO 2009-2011, foryear, the coasts of Oregon, Washington, Washington, and southern British Columbia. Particularly low oxygen is indicated by the pinks and dark blues. An isosurface key is shown southern B.C. Particularly low oxygen is indicated by the pinks and dark blues. An isosurface key is shown on the right. on the right.

2009

0 (white) 5 10 20 >20

NPUE

413


0.5

1.5

2.5

Temperature (oC)

3.5

4.5

5.5

Area 4A and 4D: 2009‐2011

6.5

7.5

Figure 4. A scatterplot of near bottom temperature (oC) versus halibut NPUE on survey stations in the Bering Sea, 2009-2011. A possible minimum temperature threshold is indicated at just under 0.5 oC.

0

5

10

15

20

25

30

‐0.5

Halibut NPUE

0 (white) 5 10 20 >20

2009

St. Matthews Island

2010

2011

Figure 5. Survey NPUE of halibut overlaid on an isosurface map of near bottom temperature (oC) for each year, 2009-2011, for the Bering Sea. The isosurface key is shown on the right. 414 IPHC Report of Assessment and Research Activities 2012