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Home , Antarctic krill

Variability in the condition of juvenile , superba, at the Western

Antarctic Peninsula

by

Radhika Shah

A THESIS

submitted to

Oregon State University

Honors College

in partial fulfillment of the requirements for the degree of

Honors Baccalaureate of Science in Environmental Science

(Honors Scholar)

March 8, 2019

Commencement June 2019 AN ABSTRACT OF THE THESIS OF

Radhika Shah for the degree of Honors Baccalaureate of Science in Environmental Science presented on March 8, 2019. Title: Variability in the condition of juvenile Antarctic krill,

Euphausia superba, at the Western .

Abstract approved:______Kim Bernard

Antarctic krill, Euphausia superba, are a highly abundant found in the

Southern . They are a key food choice for higher trophic levels and are important consumers near the base of the food web. Changes to the environment of the Western Antarctic Peninsula

(WAP), as a result of warming, are altering the marine pelagic there. The size of the krill population in the region has decreased significantly over the past 90 years. Krill preferentially select over other species; however, diatoms are becoming less abundant and are being replaced by cryptophytes and primnesiophytes. Diatoms are an important source of polyunsaturated fatty acids that krill use for growth and development. I investigated whether changes in the abundance of diatoms (using the algal pigment, fucoxanthin, as a proxy) or in sea ice conditions (timing of advance and retreat) were related to the size (dry weight) and condition

(caloric content standardized by weight) of juvenile krill. I found that there was a significant positive relationship between caloric content of juvenile krill and their dry weight. Further, my results indicated that juvenile krill caloric content and dry weight were positively correlated with a later sea ice advance and a higher abundance of diatoms. My results suggest that with continued increasing temperatures at the WAP and the predicted concurrent decline in abundance, juvenile krill will be smaller and development may be delayed. This will negative implications for the krill population as a whole. This, coupled with increased harvesting of krill by humans, could negatively impact the entire marine pelagic ecosystem. Key Words: Antarctic Krill, Western Antarctic Peninsula, sea ice duration, diatoms, Palmer

LTER, caloric content.

Corresponding e-mail address: [email protected]

©Copyright by Radhika Shah

March 8, 2019

Variability in the condition of juvenile Antarctic krill, Euphausia superba, at the Western Antarctic Peninsula

by Radhika Shah

A THESIS

submitted to

Oregon State University

Honors College

in partial fulfillment of the requirements for the degree of

Honors Baccalaureate of Science in Environmental Science (Honors Scholar)

Presented March 8, 2019 Commencement June 2019

Honors Baccalaureate of Science in Environmental Science project of Radhika Shah presented on March 8, 2019.

APPROVED:

______

Kim Bernard, Mentor, representing College of Earth, Ocean, and Atmospheric Sciences

______

Maria Kavanaugh, Committee Member, representing College of Earth, Ocean, and

Atmospheric Sciences

______

Jennifer Fehrenbacher, Committee Member, representing College of Earth, Ocean, and

Atmospheric Sciences

______

Toni Doolen, Dean, Oregon State University Honors College

I understand that my project will become part of the permanent collection of Oregon State

University, Honors College. My signature below authorizes release of my project to any reader upon request.

______

Radhika Shah, Author Table of Contents

1. Introduction ...... 8

1.1. Why the condition of juvenile krill is an important factor ...... 8 1.2. The changing WAP ...... 9 1.1.1 Sea ice 9 1.1.2 Changes at the base of the food web ...... 10 1.3. Objectives and hypotheses ...... 11

2. Methods ...... 12

2.1. Krill collection and selection ...... 12 2.2. Environmental variables ...... 13 2.3. Caloric content and dry weight measurements ...... 14 2.4. Data analysis ...... 14

3. Results ...... 15

4. Discussion ...... 16

4.1. Relationship between body size and condition ...... 17 4.2. The effect of timing of sea ice advance on the condition and size of juvenile krill .. 17 4.3. The effect of relative abundance of diatoms on the condition and size of juvenile krill 18

4.4 Management Implications ...... 19

5. Conclusions ...... 19

6. References ...... 21

7. List of Figures ...... 26

List of Tables: ...... 35

1. Introduction

Antarctic krill, Euphausia superba (hereafter referred to as “krill”), is a highly abundant and extremely successful zooplankton species in the Southern Ocean ecosystem. Its high abundance makes krill a key food choice for higher trophic levels such as , , seabirds, seals, , and (Lawson et al., 2007; Schmidt et al., 2014; Nicol, 2006). Krill are also important consumers at the base of the marine food web, feeding on a mix of diatoms, and protozoans (Kohlbach et al., 2017; Haberman et al., 2003; Stubing and Hagen,

2003). The krill population density is almost ten times higher at the Western Antarctic Peninsula

(WAP) and the as compared to the rest of (Nicol, 2006). However, environmental changes occurring at the WAP as a result of atmospheric and ocean warming are profoundly altering the marine pelagic ecosystem. In the last 90 years, the size of the krill population in this region has decreased significantly (Figure 1, from Atkinson et al., 2019). One of the leading causes is reduced sea ice which decreases production and larval and juvenile krill survival (Atkinson et al., 2019).

1.1. Why the condition of juvenile krill is an important factor

Krill condition (e.g. size and lipid content) at the juvenile stage is an important indicator of population health. Juvenile krill that are in poor condition will have low growth rates and smaller body sizes as adults (Quetin and Ross, 1991). Since the age at first spawning in krill varies by region (Ross and Quetin, 1991) and can be affected by body size (Meyer et al., 2009), a reduction in the condition of juvenile krill may also delay their reproductive development and lifelong fecundity. In this thesis, I have used caloric content per unit dry weight [Joules (mg DW)- 1] as an indicator of juvenile krill condition, where a greater caloric content per unit dry weight indicates better condition.

1.2. The changing WAP

1.1.1 Sea ice

The WAP is one of the most rapidly warming regions on the planet (Mulvaney et al., 2012;

Lima and Estay, 2013; Schofield et al., 2017). As a result of this warming, both sea ice extent and the duration of the sea ice season (determined by the timing of annual sea ice advance and retreat) are decreasing (Stammerjohn et al., 2009). Krill, with a life span of 5-7 years, rely heavily on winter sea ice, particularly at the larval and early-juvenile stages. Krill during the summer months, from December to March, and the larvae mature by fall (Fraser 1936). Larval krill must then survive the winter before they are able to recruit as juveniles into the population the following spring (Quetin and Ross, 2003). Winters with poor sea ice are commonly followed with low recruitment rates the following spring (Ryabov et al., 2017).

Juvenile krill are also better able to survive the winter with good sea ice conditions (i.e. longer duration) (Quetin et al., 1996). Juvenile krill are dependent on under-ice habitats during the winter months for food sources and protection against predators (Nicol, 2006; Schaafsma et al.,

2018; Kohlbach, 2017). Juvenile krill must survive the winter to potentially reproduce in the following spring/summer. The reproductive period for krill ranges from 1.5-3 months (Meyer,

2012) during the summer and can begin as early as age class 2 (i.e. 2-year old krill) in some regions.

The timing of sexual maturity varies by region and is likely determined by growth and development rates of juveniles. Krill seasonal growth and reproductive development cycles parallel the seasonal cycles of food supply and is it likely that regional differences in food availability may drive the differences in timing of sexual development (Daly, 1990). If juvenile krill are in good condition, they will likely be able to grow faster and reproduce sooner since they will reach sexual maturity earlier (Daly, 1990). This would benefit the entire krill population.

Previous studies suggest that a later sea ice formation may negatively impact the juvenile krill winter budget (Bernard et al., 2019). In the Bransfield Strait, northern WAP, juvenile krill were not able to meet their minimum energy demands through grazing on algae when sea ice formation was delayed (Bernard et al., 2019). However, when sea ice formation occurred relatively early, juvenile krill feeding on algae were exceeding their minimum energy demand (Bernard et al., 2019). If the timing of sea ice advance affects the winter condition of juvenile krill, then it might also affect their early summer condition.

1.1.2 Changes at the base of the food web

Studies such as the Palmer Antarctica Long Term Ecological Research (Palmer LTER) project and the Rothera Time Series (RaTS), conducted over multiple decades, have investigated the implications of and sea ice decline along the WAP in order to predict future ecosystem states (Ross et al., 2014; Rozema et al., 2017). Major changes have already been observed at the base of the food web. Specifically, phytoplankton and the prevalence of diatoms have decreased over time and are strongly correlated with a reduction in sea ice extent

(Rozema et al., 2017; Schofield et al., 2018).

Spring typically signals the growth of phytoplankton due to the emergence of light and a shallower mixed layer depth due to warming and freshening of melt water and water column stabilization (Arrigo et al., 2017; Rozema et al., 2017; Petrou et al., 2016; Saba et al., 2014). These are all favorable conditions for a successful phytoplankton bloom. Conversely, strong winds, a deep mixed layer, and minimum light availability are factors that decrease phytoplankton growth and greatly affect total biomass (Saba et al., 2014). Earlier sea ice retreat or reduced sea ice extent results in deeper wind-driven mixing of the surface waters and delayed water column stratification that negatively affects the formation of phytoplankton blooms (Montes-Hugo et al., 2009).

As diatoms are becoming less abundant, they are being replaced by other taxa such as cryptophytes and primnesiophytes (Saba et al., 2012; Rozema et al., 2017; Petrou et al., 2016).

However, krill selectively prefer diatoms over other phytoplankton (Atkinson et al., 2012; Schmidt et al., 2014; Haberman et al., 2003); thus, changes in the phytoplankton community structure may negatively affect krill. Diatoms are an important source of polyunsaturated fatty acids (PUFAs) that krill use for growth and development. However, when diatoms are not available, krill feed on other prey, such as copepods and protozoans (Petrou et al., 2016).

Studies have shown that the quality of food consumed plays a significant role in the physiology and condition of krill (Hagen et al., 2001; Schmidt et al., 2014; Schaafsma et al., 2018).

Although krill accumulate PUFAs when consuming a diet dominated by diatoms, they have a higher proportion of triacylglycerols (TAGs) when primarily consuming copepods (Hagen et al.,

2001). Unlike PUFAs, TAGs are stored by krill and not redirected to growth and development

(Hagen et al., 2001). Thus, a switch in the diet of juvenile krill from diatoms to copepods may affect both their size and condition.

1.3. Objectives and hypotheses

Here, I examine variability in the condition (measured as caloric content per unit dry weight) and body size (measured as dry weight) of juvenile krill along the WAP to investigate whether sea ice duration and diatom abundance affect either the condition or size of juvenile krill. I hypothesize that:

(1) The condition of juvenile krill increases with increasing body size. (2) The summer condition and size of juvenile krill will be negatively correlated with timing of

sea ice advance and positively correlated with the timing of sea ice retreat.

(3) The condition and size of juvenile krill will be positively correlated with the relative

abundance of diatoms.

2. Methods

2.1. Krill collection and selection

Researchers collected all krill samples and environmental data from the Palmer Antarctic

Long Term Ecological Research (Palmer LTER) project during their annual research cruises in

January from 1994-2003 at the Western Antarctic Peninsula (WAP). The Palmer LTER was established in 1990 as part of a national network of long-term ecological research sites created by the United States National Science Foundation (NSF). The Palmer LTER conducts an annual summer cruise in January each year that runs along a standard survey grid (Figure 2). For my study, I only used juvenile krill collected in 1994-1997, 2001 and 2003, because these were the years that we had enough individual specimens for analysis. The Palmer LTER grid consists of transect lines positioned 100 km apart running perpendicular to the shore, starting with -100 in the south and ending at 900 in the far north of the WAP (Figure 2). Stations are located at 20 km intervals along each transect line (Figure 2). In this study, I divided the grid into (1) the north

(transect lines 400, 500, and 600) and (2) the south (transect lines 300 and 200).

The Palmer LTER collected zooplankton using a 2x2 m square mouth net, towed obliquely from the surface to 120 m depth at each station. Krill were counted and their lengths were measured using Standard Length 1 after Mauchline (1980). Krill were then placed into individual scintillation vials and frozen at -80˚C for later analysis. From each year, I selected between 5 and 9 individual krill (Table 1; 27-31 mm in length) from stations occupied in both the north and south of the WAP for further analysis of their condition.

I used caloric content standardized by dry weight [Joules (mg DW)-1] as a proxy for krill condition. I selected only juvenile krill between 27-31 mm of length for this study because individuals larger than 31 mm may have already begun reproductive development and thus would not be considered juveniles. Further, by using only juvenile krill, I avoided any biases associated with variability in caloric content with later life stages. In particular, adult female krill have high caloric contents when they are reproductively active in the spring and summer (Ruck et al., 2014).

2.2. Environmental variables

Relative abundance of diatoms: In order to estimate the relative abundance of diatoms to the total phytoplankton community, I used high-performance liquid chromatography (HPLC) data collected by the Palmer LTER (Schofield et al., 2017). Specifically, I used the relative concentrations of the accessory pigment, fucoxanthin, a chemotaxonomic marker of diatom prevalence. Fucoxanthin is also present in other phytoplankton taxa, such as prymnesiophytes, raphidophytes and chryophytes (Kavanaugh et al., 2015), however in this region and period of time, diatoms would have been the only major phytoplankton taxa with fucoxanthin (Kavanaugh et al., 2015). This is because the raphidophytes and chryophytes do not have high population densities along the WAP and prymnesiophytes have undetectable concentrations of fucoxanthin, particularly under -limitation (Kavanaugh et al., 2015). The Palmer LTER researchers measured phytoplankton pigments on whole seawater samples collected throughout the water column at each station (Moline & Prézelin, 1996). Concentrations of chemotaxonomic markers

(e.g. fucoxanthin) and total chlorophyll-a (Chl-a) were determined by the Palmer LTER researchers using ChemTax (Mackey et al., 1996, 1998). The relative contribution of diatoms to the overall phytoplankton biomass was calculated as the percentage of fucoxanthin to total Chl-a

(Moline & Prézelin, 1996).

Timing of Sea Ice Advance and Retreat: I obtained sea ice advance and retreat data from the Palmer LTER data archives (Stammerjohn, 2017). Sea ice advance and retreat is calculated by the Palmer LTER within a given sea ice year using passive microwave satellite measurements. The anomaly for both day of sea ice retreat and advance was calculated for the north and south region.

This was done by subtracting the value from the mean for that region (either the north or south), calculated for the period of 1979-2016 based on available Palmer LTER data. The anomaly was used instead of the actual value because sea ice will always retreat earlier and advance later in the north compared to the south.

2.3. Caloric content and dry weight measurements

I used bomb calorimetry (Figure 3) to analyze the caloric content of the juvenile krill. Bomb calorimetry calculates the amount of energy per unit mass by measuring the amount of heat that is released when the sample becomes completely oxidized (Schaafsma et al., 2018). To prepare the juvenile krill samples for caloric content [CC, Joules (mg DW)-1] measurements, I first dried them in an oven at 60˚C for 48 hours before weighing them to obtain dry weight (DW, mg) and then grinding each individual krill using a pestle and mortar. Using a pellet press, I pressed each homogenized krill sample into a pellet. The pellet was then placed into the combustion capsule in the bomb calorimeter. The combustion capsule is attached to fuse wires, and these together are placed into the bomb cell (Figure 3).

2.4. Data analysis

A two-way analysis of variance (ANOVA) was used to test for any significant differences in either the CC or DW of krill by region (northern versus southern WAP) or year. Since there was no significant difference for either CC or DW (see Results section), I subsequently conducted all further analyses used both the north and south data combined. A Model II linear regression was used to test whether CC of juvenile krill was significantly related to DW. The Model II linear regression was used instead of the Model I since the x-axis variable, DW, is random and not fixed

(Quinn and Keough, 2002). The Geometric Mean Regression Method was utilized because the units and the range for the CC and DW are different (Ricker, 1973).

The predictor variables I was interested in included day of sea ice retreat anomaly, day of sea ice advance anomaly, and the percent of fucoxanthin to total Chl-a. However, all these variables are also random and are not fixed, thus Model II linear regressions were appropriate.

Model II linear regressions with multiple predictor variables can be achieved by creating a new predictor variable using Principal Components Analysis (PCA) that includes all of the original predictor variables. The first principal component of the PCA can serve as the new predictor variable. In order to test whether day of retreat anomaly, day of advance anomaly, and the percent of fucoxanthin to total Chl-a had significant effect on CC or DW, I ran a PCA using all three predicator variables. Then, I ran a Model II regression using the Geometric Mean Regression to test whether there was a significant relationship between either CC or DW and the score of the first principal component.

3. Results

Caloric content (CC) of juvenile krill ranged between 16.13 and 23.88 Joules (mg DW)-1

(mean = 21.03 Joules (mg DW)-1; SD = 0.01 Joules (mg DW)-1). The mean CC of juvenile krill from the northern WAP (21.05 Joules (mg DW)-1) was not significantly different (p = 0.73) from the mean value in the southern WAP (21.00 Joules (mg DW)-1; Figure 3.A). Although CC of juvenile krill varied from year to year, there was no significant difference in CC between the years examined in this study (p = 0.90; Figure 4.A). Similarly, although dry weight (DW) of juvenile krill examined in this study was variable (44 mg to 57 mg), there was no significant difference in

DW either by region (p = 0.87; Figure 3.B) or year (p = 0.48; Figure 4.B). There was a significant positive relationship between CC of juvenile krill and their DW (p < 0.001, Figure 5).

The first principal component of the PCA is driven largely by the percent of fucoxanthin to total Chl-a and, to a lesser degree, by day of sea ice advance anomaly (Figure 6). Model II linear regressions showed that both CC (p < 0.001; R2 = 0.569; Figure 7.A) and DW (p < 0.001; R2 =

0.382; Figure 7.B) of juvenile krill were significantly positively correlated with the score of the first principal component of the PCA. Since the first principal component is driven by positive fucoxanthin percentages and day of sea ice advance anomaly, the relationship between CC and

DW and the first principal component indicates a positive relationship of these two variables with both fucoxanthin proportions and timing of sea ice advance.

4. Discussion

I examined the variability in caloric content (CC) and dry weight (DW) of juvenile

Antarctic krill and assessed whether CC was positively correlated with DW. In addition, I investigated whether the timing of sea ice advance and retreat or the percent contribution of diatoms to total Chl-a were significant drivers of the condition (i.e. CC) or size (i.e. DW) of juvenile krill. There are three main conclusions of my work. First, the condition of juvenile krill increased significantly with increasing body size. Second, the condition and size of juvenile krill were greater with a later sea ice advance. Third, both the condition and size of juvenile krill were positively correlated the percent contribution of diatoms to total Chl-a. Below, I discuss the implications of these findings in further detail. 4.1. Relationship between body size and condition

The relationship between juvenile krill body size and condition is important because it emphasizes the role of body size in overall condition; larger juvenile krill are in better condition.

This relationship may also be indicative of earlier reproductive development in larger juvenile krill. Studies suggest that the age of first spawning in krill varies with region (Ross and Quetin,

1991). It is possible that under conditions that favor increased growth and therefore larger sizes in juvenile krill reproductive development may be initiated earlier (Meyer, 2009). Since reproductive development results in an increase in caloric content (Meyer, 2012), we can expect that earlier initiation of reproductive development in larger juvenile krill would be associated with higher caloric contents. If krill experience better conditions for growth and are able to initiate reproductive development earlier, it might benefit the entire krill population.

4.2. The effect of timing of sea ice advance on the condition and size of juvenile krill

Previous studies have suggested that sea ice is important for the survival of both larval and juvenile Antarctic krill during the winter months and their subsequent recruitment the following spring (e.g. Saba et al., 2014; Kohlbach et al., 2017). Because juvenile krill are not able to store as much energy as adult krill, they rely on sea for feeding during winter months (Meyer et al., 2002). It has been suggested that a later sea ice advance will negatively affect overwintering krill by resulting in reduced ice algae availability (Meyer, 2012). However, while later sea ice advance means less algae for the winter, this did not result in reduced condition or body size of juvenile krill in the summer in my study. One possible reason for this is that with delayed sea ice advance and consequently reduced ice algae available to overwintering larvae, there might be fewer juvenile krill recruiting into the population and therefore less competition for food in the subsequent spring and summer. While early sea ice advance is typically associated with the development and growth of the rich ice algae biomass that is a key food source for overwintering larval and juvenile krill, the development of a strong spring-summer phytoplankton bloom is likely a better indicator of juvenile krill condition and body size in January, when our samples were collected. Indeed, I found a significant relationship between percent contribution of diatoms to total Chl-a (i.e. their relative abundance) and the condition and size of juvenile krill.

4.3. The effect of relative abundance of diatoms on the condition and size of juvenile krill

I found that, with increasing relative abundance of diatoms, juvenile krill were not only larger, likely due to eating PUFA-rich diatoms, but they were in better condition (i.e. had higher

CC). I argue that this association was likely due to the juvenile krill feeding preferentially on the available diatoms. Krill are known to favor diatoms because of their larger size (Haberman et al.,

2003) and nutritional quality (Montes-Hugo, 2009). Since diatoms are a good source of PUFAs, which are used by krill for growth and development, a diet rich in diatoms will contribute to the growth and, potentially, earlier reproductive development of juvenile krill, which may result in higher caloric content. Indeed, I also found a clear positive correlation between the condition and body size of juvenile krill. When diatoms are not available, krill shift their diet to other food sources such as copepods, which contain triglycerides, TAGs (Atkinson et al., 2012). Unlike

PUFAs, TAGs are stored by krill instead of being used for growth. Thus, juvenile krill feeding on copepods may experience delayed maturation (Meyer, 2012).

My results suggest that a diet of diatoms is physiologically advantageous to juvenile krill and that future predicted changes in the phytoplankton community at the WAP may have a negative effect on their condition. 4.4 Management Implications

There is a rapidly growing fishery for Antarctic krill that is centered along the WAP and into the Scotia Sea (Nicol et al., 2011; Hill, 2013). A reason for this renewed interest in Antarctic krill is because of developments in harvesting technology and in products using krill derivatives

(Nicol et al., 2011). In this time of rapid climate change, it is critical that we understand as much as possible about the Antarctic krill population and how it is changing so that we are able to effectively manage the .

These results are beneficial to the management of the krill fishery since juvenile krill are not usually studied. Instead, mature adults are focused on by fisheries managers. Understanding juvenile krill condition is essential for predicting future population size so that managers can place restrictions on harvest, if needed.

5. Conclusions

To conclude, I found the following major results:

1. The condition of juvenile krill increases significantly with increasing body size. It is

possible that larger juvenile krill initiate reproductive development earlier than their

smaller counterparts, resulting in their higher caloric content.

2. The condition and size of juvenile krill is greater during summers that follow a later sea ice

advance. A later sea ice advance would result in reduced overwinter survival of larval krill,

and consequently fewer juveniles recruiting the following spring. This would mean less

competition for food in the spring and summer months.

3. The condition and size of juvenile krill is positively correlated to the relative abundance of

diatoms. A shift in phytoplankton community structure in which diatoms are less prevalent

will negatively affect the condition of juvenile krill.

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Antarctic Peninsula derived from passive microwave satellite, 1978 - 2016. Environmental Data

Initiative. Turner, J., et al. (2013). "The impact of changes in sea ice advance on the large winter warming on the western Antarctic Peninsula." International Journal of Climatology. 33(4):852-861. 7. List of Figures

Figure 1: Maps indicating the southward contraction of krill distribution within the Southwest Atlantic sector of the Antarctic Peninsula (from Atkinson et. al, 2019). Figure 2: Map of the Palmer LTER regional grid, indicating transect lines and stations where samples used in my study were collected. The red star indicates Palmer Station. Figure 3: Drawing of a bomb calorimeter showing the components that contribute to the set up. Not shown in the diagram is the oxygen tank that transfers gas to the bomb cell and sample once ready for measurement. Figure 4: Regional variability in (A) average caloric content [Joules (mg DW)-1] and (B) average dry weight (mg) of juvenile krill in the northern and southern WAP. Error bars are standard error. Figure 5: Inter-annual variability in (A) average caloric content [Joules (mg DW)-1] and (B) average dry weight (mg) of juvenile krill between 1994 and 2003. Northern samples are in green, southern samples are in blue. Error bars are standard error. Figure 6: Model II linear regression of dry weight (mg) of juvenile krill with caloric content [Joules (mg DW) -1]. Figure 7: Results of the Principal Components Analysis. DAdvAnom = day of sea ice advance anomaly; DRetAnom = day of sea ice retreat anomaly; Fuc = fucoxanthin proportion. Figure 8. Model II linear regression of (A) average caloric content [Joules (mg DW)-1] and (B) average dry weight (mg) of juvenile krill with the first principal component of the PCA.

Figure 1

Figure 2 Figure 3: Figure 4

Figure 5

Figure 6

Figure 7

Figure 8 List of Tables:

Table 1: Number of krill used in the North and South for each individual year Table 1 :

Year Region Krill Count 1994 North 8 1994 South 5 1995 North 7 1995 South 6 1996 North 9 1996 South 7 1997 North 8 1997 South 6 2001 North 6 2001 South 6 2003 North 7 2003 South 6