Response to REVIEWER #2 evaluation of manuscript – Fisheries Oceanography
Manuscript number: ___Fisheries Oceanography 040480_____
Author(s): __ Trites et al. ______
Title: “Bottom-Up Forcing and the Decline of Steller Sea Lions in Alaska: Assessing the Ocean Climate Hypothesis”
Referee: __ Reviewer #2______
Signed _[S] Patricia Livingston______Date _____4 Nov 2004______
We thank Dr. Livingston for the excellent comments that helped us to significantly improve the paper.
Comments:
Overall, I find the idea of the review paper very commendable. The attempt to synthesize a somewhat diverse set of studies in an attempt to evaluate broad scale climate patterns relative to sea lion declines is a good idea. However, I found that the conclusions of the individual sections, which were in many cases equivocal with regard to a link to sea lion decline or diet, and the ending conclusion that climate is the only major driving force that can link so many changes does not seem very supportable.
Each section now has a concluding paragraph to link back to this point.
There is disregard for the tremendous amount of work that went into the NRC 2003 synthesis of hypotheses and evaluation of research to support the hypotheses in that the paper begins with a listing of leading hypotheses that don’t really match the hypotheses as set out by NRC. Although NRC also concludes (as does this review) that the rangewide declines from 85-89 were likely caused by an ecosystem wide change in the sea lion environment (but also implicating incidental and deliberate human induced mortalities), it concluded that bottom up forces were unlikely to be preventing the recent (1990 to present ) lack of recovery. I recommend a closer reading of the NRC report and the Is it Food II (2001) report and making sure the conclusions of those groups of experts are also discussed more thoroughly relative to the findings of this review.
DeMaster et al. (in review) recently wrote “the conclusion drawn by the NRC panel on the decline of the western population of Steller sea lion (NRC 2003) that there is no evidence for nutritional stress in the 1990s in this population appears to be in error.” We state a similar conclusion regarding the NRC review and have expanded on this with the addition of two paragraphs on Page 6.
The paper also does not fully address the goals stated on page 4 second paragraph, which were to determine whether there were any spatial or temporal patterns in phys and biol data that corresponded to differences in the diets and number of sea lions since the late 50s, and secondly to put the recent decline in context with the similar changes occurring over the past 4000 years. Particularly, the first goal needs more work. The abstract never mentions any results that might relate to diet differences and similarly the summary does not include any mention of that link.
Sentences have been added to the abstract and summary to emphasize the link between diets and the temporal and spatial patterns in physical and biological data.
I thought there was too much unnecessary detail contained in the results and descriptions of individual studies and some figures could be omitted.
Text has been sharpened and half of the figures have been deleted.
Although I understand that the main purpose is to summarize the CIFAR-funded research, there is not enough discussion of their results relevant to specifics about the sea lion decline. There is a section summarizing Steller sea lion studies, the paper then moves into individual summaries of the CIFAR projects (which do NOT then make any link between their results and any of the sea lion trends mentioned previously), then the paper ends with a summary that also fails to provide any discussion of the results relative to sea lions. I recommend more work by the authors to more clearly and succinctly summarize their research results and discuss how those results relate to the goals stated on p. 4.
We have tried to make stronger links between sea lions and the relevant CIFAR research findings by including concluding paragraphs that link back to this point.
Sometimes individual studies mention further research needs, and sometimes they don’t. I would also recommend providing a more comprehensive listing of further research needs at the end of the paper, instead of the disconnected items listed in the individual research project results.
Adding a list of recommendations for future work would change the purpose of this paper. To maintain consistency between the sections, we have removed all recommendations.
Here are some further editorial remarks that relate to specific parts of the text/tables/figures:
1) abstract lacks mention of links, if any, between climate and sea lion diet.
This is now added.
2) conceptual figures and text don’t seem to mention direct effects of climate on metabolism, etc. of Steller’s – is this important?
It is very unlikely that changes in water temperature would have a significant effect on metabolism. This is based on studies with Steller sea lions at the Vancouver Aquarium where heat flux and metabolism have been measured as water temperature has been changed. Steller sea lions appear to have quite a wide thermal neutral zone.
3) pg 3, para 2, Check listing of “leading hypotheses” here relative to NRC’s list
All of the hypothesis we list are contained within the NRC report, with the exception that the NRC report failed to define ‘nutritional stress’ and appear to have assumed that it only meant starvation. The subtleties of the nutritional stress hypothesis are reviewed in Trites and Donnelly (2003).
4) pg 4, para 2, these objectives are not fully discussed in summary or abstract
This has now been clarified.
5) pg 7, para 2, Change leading sentence to something more like “An important driving force that could account for the geographic and temporal differences noted in sea lion diets, and some of the declines in numbers are spatial and temporal differences in ocean climate.”
Done.
6)pg 8, para 2, there are relevant examples on how large-scale climate affects local populations. See Wilderbuer et al. 2002: BS flatfish example:
Wilderbuer et al. presented a “mechanistic” explanation for the decadal variability of three Eastern Bering Sea flatfish stocks: flathead sole, northern rock sole, and arrowtooth flounder. They invoked spawning stock and shoreward wind-driven advection of larvae as the primary determinants of productivity. The point seems to be that there have been some attempts at explaining the observed decadal variability.
We now mention in the text that there are proposed mechanisms, but none yet that have truly been tested and validated with field studies.
7) pg 8, para 3, too jargony refs to Trend-1, Trend-2, etc. Make more clear to broad audience.
This has been cleaned up.
8) pg 9, para2, first sentence “the ocean temperature data show temporal and spatial patterns ….that may be correlated…” Was this correlation done? I didn’t see the results of this.
Text now states “visually correlated”.
9)pg10, last para, again jargony refs to names of principle components. Abbreviation of PC not defined.
This has been cleaned up.
10)pg 11, para 3, wavelet analysis – many people don’t know what this is.
This has been deleted.
11) pg 15, para 1, need clearer explanation here of disccusion of model diffs relative to observations
This has been re-written, including response to Referee 1.
12) pg 15, para 3, what link is there between this info on sea ice-ocean model to sea lions?
Link to biology is now mentioned.
13) pg. 19 last sentence, “Abrupt population increases in flatfish” these increases were not abrupt but increasing in a decadal fashion due to positive recruitments
“Abrupt” has been dropped and the sentence clarified.
14) pg. 20, para 1, “The composition of trawl catches” should be “The composition of trawl catches in this survey” so people don’t think it was fishery observation.
Changed as suggested.
15) pg 20, para 2, “The links between climate and population size is at the recruitment stage” should be modified to something like “An important link between climate and population size occurs at the larval and juvenile stages for many marine animals (refs).
Done.
16)pg 23, para 2, ref to Trites et al 1999 not correct in this context.
Anderson (2000) and Anderson and Piatt (1999) are a better citation regarding changes in shrimp populations and are now cited.
17) I ran out of time to look at all the figures in detail but suggest that many are not necessary. Some potential candidates for removal include: fig2 and 23: consolidate into one?; fig 5 remove, fig 6and 7: pick one, fig 8: remove; fig 9 and 10 remove, fig 14 remove, fig 15 remove; fig 16 remove; fig 20 remove;
Most of these have been removed as suggested.