Milldaz Goes Nørther: Our Mission Part 3: The Why

It’s the final night of our research cruise and I haven’t yet explained fully why we did it exactly, and in particular why I am here instead of some well-trained monkey. Those of you who have been reading the blog will have some vague idea about how it serves some role in fisheries management, but now I will now try to fill in some of the blanks, a simply as possible.

Fish stocks are what we call ‘living marine resources’. These are natural resources that, if not managed sustainably, can be destroyed beyond repair. To put it in financial terms, to utilise a natural resource sustainably is like living off the interest from an investment, rather than digging into the capital. To put it in fairy-tale terms, it’s like selling the golden eggs, not slaughtering the goose. The problem is, when it comes to most marine resources, finding how much capital you’ve got is not as simple as looking at a bank balance (or counting one golden goose). In many cases it’s impossible to ever truly know exactly how much of the resource is there, let alone how much of the resource the environment can support. An old fisheries joke puts it best I think: “Counting fish is like counting trees, except you can’t see them and they move around”.

So how do we attempt to measure our natural capital? Here’s a simple example. Let’s say you went for a week long holiday to a large lake and did some fishing. Every day at 5am you get up, go to a different spot around the lake and fish for 6 hours. You use the same tried and tested bait, and the same rod and reel you’ve had for years. Nothing fancy. By the end of the week you have managed to fish at spots all around the lake, and you caught 100 fish. Good going. The next year you return to the same holiday house (who wouldn’t after catching 100 fish the year before?) and follow the same procedure. You use the same gear and bait, fish at the same time of day, for the same amount of time, at the same 7 spots. Only this time by the end of the week you have only caught 75 fish. You’ve only spent one week there, but all year round there is a medium sized fishery that operates on the lake. You check the local paper and see that last year the local fish market sold 1000t of fish, all form local fishermen.

Here’s a picture of a boat to break up the monotony of all this text:

Off To The Oil Rig With You

You now have the basic ingredients for a fisheries model to predict the amount of fish in the lake. Your fishing trips form a good survey: widespread coverage, constant effort, and the same methods year to year. From this short ‘survey’ you can deduce that the population of fish in the lake reduced by 25% last year (your catch went from 100 down to 75, a 25% drop). You know that the fishery is the major remover of fish and you have a good estimate of what they took. So you can use this number to scale up your relative index: the 25% reduction must have been because of the 1000t they took. If 1000t = 25%, then there must have been 4000t in the first year, and 3000t in the second year. 4000-3000=1000t, and this is a 25% reduction.

Of course, there is more to it than that. Aside from the fact that no survey or catch data are ever perfect, each year new fish are born and fish die of natural causes too, not just because of fishermen. There may be other sources of mortality, maybe the new nuclear plant that opened up on the far bank has something to do with the decline. But as a simple example it illustrates the main sources of information we need to do proper fisheries assessments: an unbiased, relative index of abundance (your fishing trip catches) and precise and accurate information on removals from the population (the fishery catch).

Blinky: Animation’s Finest Example Of Nuclear-Impacted Fisheries

The first of those two is why we are here: to get a relative index of the abundance of herring. Only we don’t fish for the herring, they are far too widely distributed and migratory for that. That’s where acoustics is a vitally important tool. We can cover a very broad area much quicker than if we had to stop and fish at certain places all the time. I have made various jokes about well-trained monkeys doing this work, but that does a massive disservice to those scientists and engineers who have dedicated their whole careers to the development and practical implementation of acoustics in fisheries science. I just did the easy application part.

It is actually lucky for us that herring can be surveyed using acoustics, because for certain other fish species, such as Mackerel, this method is ineffective. Mackerel lack a swimbladder making them much harder to detect using sonar. For Mackerel there have been attempts to 'count' them from airplanes, but we have been forced to settle on using an egg survey every three years, and estimating from that how many fish must have been there to produce those eggs. It’s not ideal. Like another old joke goes: how do you work out how many sheep are in a field? Count all the legs and divide by four. Seems unnecessarily complicated. In the case of Mackerel it’s more like count all the eggs and divide by a few million.

Acoustics isn’t perfect, but it is not so critical that we know exactly how many are there. The important thing is the need for an unbiased relative survey of abundance that is carried out in the same way from year to year. We’re not hunting out fish, just scanning the same widespread track in the same way every year and seeing how many fish are there. One of the most common complaints I hear from fishermen representatives is “You scientists don't know how and where to fish, of course you catch small amounts. Then you say the stock is small.” But we are not trying to catch as may fish as possible, we are trying to get a good relative measure of how many they are. It not about whether we catch a lot or a little, it’s about how it changes from year to year. If you purposefully search out fish instead of following a pre-specified survey plan then the measure will not be truly relative because other factors come into play, such as the captains skill in actually finding them and luck.

We found no herring this leg of the survey. None. Neither did the Norwegians find any north of 70 degrees. But there was herring further south, just this year they didn’t extend as far north at this time of year. We still had to carry on looking though, even though we all stopped expecting to find any after a few days. In this way we get further information about the stock beyond our relative index of abundance. For example we can learn how the herring stock is changing its distribution over time. This year there were none up north, next year there may be a lot. This kind of thing can be useful in ecological studies, such as examining the impact of climate change on fish populations. The initial response of a lot of stocks to changing environmental and oceanographic conditions is to change their distribution to keep within their comfort range.

Herring Distribution: Varies

Fisheries modelling is a little more complex than the lake example I gave. There are more sources of data, more mathematical gymnastics, more assumptions, and a lot of uncertainty in all of these. Dealing with this uncertainty is not always possible in a perfectly objective manner. Because herring is a straddling stock, numerous countries have a vested interest in its management. Therefore it is important to have a consensus view on what state the stock is in, and what level of pressure the fishery is putting on it. Enter the International Council for the Exploration of the Sea (ICES).

ICES: Old

ICES is an intergovernmental organisation based in Copenhagen, that, in my opinion, has an awesome name. Very adventurous. It is the oldest intergovernmental science organization in the world, having been established in 1902. This number even used to be the alarm code for the door to ICES headquarters in Copenhagen. It’s eventually been drummed into my head but at first I could never remember it. Every time I would check in: “You know the code?”, “Sure, year ICES began, 1904 or something”, “Sigh. It’s 1902!”, “OK.”, “Don’t you know your organisation?”, “No.”. Anyway, its changed now, so if any of you were planning on breaking in there to steal confidential information on the biomass of herring in the Norwegian Sea, think again.

Its members include all the nations with direct interest in the fisheries in the northeast Atlantic, the Baltic and the North Sea. ICES provides a platform for scientists from all these countries to gather together to discuss the findings, see the model fits, and to agree as one on an official line of advice to provide given the data available. This job is obviously easier the better the data is. There are various such expert groups that meet on an annual basis to discuss survey design, co-ordinate data collection, do the actual stock assessments, review these assessments, and finally draft official advice. This ICES advice is very often the primary source of scientific advice provided to managers that regulate the fisheries (e.g. the European Commission).

Atlanto-Scandian herring is dealt with at the WGWIDE expert group (Working Group on WIDEly distributed and highly migratory stocks). Here we take the data from this cruise, and a number of others, as well as all other relevant information, such as catch data, and produce an assessment of the stock. This group deals with relatively few stocks, but they are very large so by quantity of landed fish it covers more than all of the other groups combined. It is also a politically sensitive group because of the widespread nature of these stocks. Attendees range from Russia to Portugal and cover almost every coastal nation in between.

For the last two years I have attended this working group as one of the Dutch representatives, given that I currently work at the Institute of Marine Resources and Ecosystem Studies (IMARES) in IJmuiden, Netherlands. At last year’s meeting I was elected as chairperson of this group for the next three years. This despite being the youngest there and the only one from a different hemisphere. Admittedly that puts me a little out of touch with these stocks compared to the selection of experts there. That is why I am here on this cruise now: trying to get a feel for the situation on the ground, or in the water, as it were. My true area of expertise is as an end user of data, less so on the collection side as we are doing on this survey. But it is important to have a good feeling for how it is garnered. It is also good to have a feeling for the history and importance of the work you do, as well as where it fits into the whole process. The overall experience, more than any particular things learned, will prove valuable in developing my understanding of this stock and the data we have on it, as well as improving how I approach and execute my work.

Back To The Office To Put This Data To Use

In addition to the Atlanto-Scandian / Norwegian Spring Spawning Herring, the group also deals with Northeast Atlantic Mackerel, Blue Whiting, Horse Mackerel (two stocks) and starting this year, two boarfish stocks. You may recall from earlier that blue whiting is currently a stock in dire straits. I am already very involved, together with fisheries industry representatives and scientists from Norway, Ireland and the UK, in working towards a new assessment of blue whiting as well as developing a management plan suitable to deal with the particular dynamics and uncertainties of this stock. Mackerel is a particularly sensitive subject amongst the Icelanders, Faroeses and Britain as the stock is changing its distribution and spending more time in Icelandic and Faroese waters than previously, so they are after a greater share of this resource. Boarfish is controversial in that not long ago it was a species that you avoided like the plague because it clogged up nets and pumps and had seemingly little value. Now the Danish and the Irish are getting quite keen on it. Some of the more environmentally minded could feel that this is a classic case of moving on to less desirable species because other stocks have been fished down, a slippery path to get on. Others may argue it is a natural expansion of operations. Horse Mackerel just has weird population dynamics.

In a way it is good that I am not a super-expert on any of these species. The large uncertainties in fisheries science often require broad brushstrokes to be made, rather than fine detailed analysis. Multiple sources of often conflicting information need to be tied together and synthesised into something that is actually useable in a management sense. Managers want clean clear graphs like the ones below, not long convoluted statements about how the herring were a little depressed this year and spawned less.

The Herring Are Alright

Clear signals are needed, to which management can react. But these signals need to be relevant and truly indicative on what is happening out in the ocean. Somebody too focussed on the specifics of particular stocks could have a harder time overlooking the finer details. Of course, knowing your stock is very important, particularly when it comes to gaps in the data, or unexplained anomalies. I am learning more every day, through experiences like this.

And that is why I am here.

All this talk of fisheries management and mathematical modelling obviously doesn’t come with a whole lot of interesting photographs. So I will finish this post with a few more pictures of some of the more popular entries in this blog so far. Here’s some more of the lumpsuckers: