SC/61/JR3 (additional analysis -SC/J09/JR23)

Additional analyses of temporal trends and factors affecting
mercury levels in common minke, Bryde’s and sei whales inthe western North Pacific
GENTA YASUNAGA AND YOSHIHIRO FUJISEThe Institute of Cetacean Research, 4-5 Toyomi-cho, Chuo-ku, Tokyo, 104-0055, Japan.
Contact e-mail: yasunaga@cetacean.jp
ABSTRACTThis short paper presents an additional analysis on total mercury (THg) trend in common minke whale from the western
North Pacific in response to some recommendations from the JARPN II review workshop. Specifically a generalized
additive model (GAM) analysis was recommended to examine temporal trend of THg levels in common minke whales
from sub-area 9 in the period 1994-2007. Results of this analysis suggest two periods: the first extending until 1999
showing a decreasing trend and a second from 2000 showing a stable trend. These results based on GAM are the sameas those obtained in the original paper based on multiple linear regression analyses (Yasunaga and Fujise, 2009)(SC/J09/JR23). In response to other recommendation, a schematic figure on total Hg (THg) flow in the western North
Pacific food web is presented and described in this paper.
INTRODUCTION
The International Whaling Commission’s Scientific Committee (IWC SC) carried out a Workshop to review theprogress made in the research conducted under the Japanese Whale Research Programme under Special Permit in theNorth Pacific-Phase II (JARPN II) in its first six years (2002-2007). The review was carried out by an Independent
Expert Panel (IEP) who examined primary papers related with the research objectives of JARPN II.

One of the objectives of the JARPN II is ‘Monitoring environmental pollutants in cetaceans and the marine ecosystem’
and regarding to this objective three primary papers were presented to the review workshop. Yasunaga and Fujise(2009) examined temporal trends and factors affecting mercury levels in common minke, Bryde’s and sei whales andtheir prey species in the western North Pacific (SC/J09/JR23). Regarding whales, apart from common minke whales
from sub-area 9, significant yearly changes of mercury levels were not observed. For minke whales in sub-area 9, levels
decreased from 1994 to 1999 but increased from 2000 to 2007. Results of a multi linear regression analysis suggested
that changes of mercury levels in sub-area 9 reflected changes in food habit rather than changes in accumulation levelsin the environment.
During the review workshop the IEP recommended that ‘a generalized additive model (GAM) fitted to these data would
be a better method for determining the change points and examining non-linear trends in the Hg levels’ (IWC, 2009). In
response to such a recommendation an additional analysis based on (GAM) was conducted to determine the changepoints of Hg levels in muscle of common minke whales from sub-area 9 during the period 1994-2007. In addition theIEP recommended that a schematic figure on total Hg (THg) flow in the western North Pacific food web be added inany future paper (this figure was introduced in the Power Point presentation but not in the original paper). This figure isadded and described in this paper.
MATERIALS AND METHODS
Muscle tissues from mature males of the common minke whales (Okhotsk Sea-West Pacific stock) from sub-area 9
were collected by JARPN II researchers in the surveys conducted in the period from 1994 to 2007. The GAM analyses
were executed by R software (R Development Core Team, 2006). A more detailed description of the materials andmethods used in the study is provided in the original paper by Yasunaga and Fujise (2009) (SC/J09/JR23).
RESULTS AND DISCUSSION
Figure 1 shows the relationships between THg levels in muscle of minke whales and sampling year. Figure 2 shows its
smoothing curve using GAM. A changing point of THg levels were observed during 1999 and 2000 (Figure 2).
Therefore, it is reasonable to distinguish between two periods for the THg levels in common minke whales from subarea 9: the first extending until 1999 shows a decreasing trend and a second from 2000 shows a stable trend. Theseresults based on GAM are the same as those obtained in the original paper based on multiple linear regression analyses(Yasunaga and Fujise, 2009) (SC/J09/JR23).

A schematic figure of total Hg flow in the western North Pacific food web is shown in Figure 3. This figure indicatesthat differences in food habitat explain the pattern of Hg accumulation of baleen whales.
REFERENCES
International Whaling Commission. 2009. The Report of the Expert Workshop to review the ongoing JARPN II
Programme. Document SC/61/xx presented to this meeting.
R Development Core Team. 2006. R: A language and environment for statistical computing. R Foundation for
Statistical Computing, Vienna, Austria. ISBN 3-900051-07-0, URL http://www.R-project.org.
Yasunaga, G. and Fujise, Y. 2009. Temporal trends and factors affecting mercury levels in common minke, Bryde’sand sei whales and their prey species in the western North Pacific. Paper SC/J09/JR23 presented to theJARPN II Review Workshop, Tokyo, January 2009 (unpublished). 14pp.

Hg (ppm wet wt.)

1.00
0.75
0.50
0.25
0.00
1994

1996

1998

2000

2002

2004

2006

year

0.05
-0.05
-0.15

Mercury

0.15

Figure 1. Total mercury (THg) levels in muscle of mature common minke whales in sub-area 9
during the period 1994-2007. This is a corrected figure of that presented in Yasunaga and Fujise(2009) (SC/J09/JR23) as Figure 6.

1994

1996

1998

2000

2002

2004

2006

YEAR

Figure 2. Smoothing plots of total mercury (THg) levels in muscle of mature common minke whales in sub-area 9
against research years for the period 1994-2007 using the generalized additive model (GAM).

230.1

0.2

0.3

0.4

0.5

Bryde’ sSei
Saury

Pelagic fishes
Anchovy
Anchovy
Saury

Zooplankton

Plankton feeders

PomfretMesopelagic
fishesCoastal minke whale

Offshore minke whale

Figure 3. Schematic figure of total Hg flow in the western North Pacific food web.

Seawater(c.a. 1.7pM)

THg levels (ppm wet wt.)