Consistency is Key in Measuring Fish Abundance

Have you ever wondered how fish populations are measured?

With countless factors impacting abundance, such as changing ocean and ecosystem conditions, predator-prey relationships, mortality and recruitment rates, fishing pressure and the interconnected nature of the ecosystem — figuring out how a species is fairing is a complicated task.

Fisheries and Oceans Canada (DFO) conducts annual at-sea surveys to collect data that are later analyzed in its labs to ultimately answer the question — has the fish population improved, declined or stayed about the same year over year.

There is a lot of coordination and logistics that must take place before, during and after scientists go to sea, which is in addition to the time and effort invested in keeping their data collection work exactly the same.

George Sheppard, science facilities manager

George Sheppard is a science facilities manager with DFO and plays a key role in survey logistics and maintaining uniformity among how various scientists conduct their work on scientific surveys.

“We’ve been successful in keeping this work consistent for 40 years and are working very hard to ensure this continues into the future.”

This consistency is so important because it allows scientists to compare the current status of fish stocks to what they were over the past few decades. Basically, it allows them to compare apples to apples.

The largest survey conducted in the Newfoundland and Labrador region is the multi-species survey.

Each year there is one multi-species survey in the spring and one in the fall — both are three months in duration. In the spring they’re focused on the areas south and south-east of Newfoundland and in the fall, they cover a larger area — from the southern Grand Bank to Nain Bank.

They collect data from locations ranging from relatively close to the coast (e.g. five to 10 nautical miles) out to depths of 1,500 metres.

DFO uses two Coast Guard vessels for the multi-species survey: the CCGS Alfred Needler and the CCGS Teleost. Most of the missions are 14 days at sea. These vessels each work over 290 days per year, conducting a variety of science programs across the marine regions of Atlantic Canada.

Modified shrimp trawl net, Campelen 1800

During the multi-species survey, a modified shrimp trawl net, Campelen 1800, is used to collect a sample of the species found in a given area near the bottom of the ocean. In order to make direct comparisons, researchers must conduct the survey at the same time of year, in the same areas, use the net in exactly the same way and keep their work consistent. This enables them to compare data collected today to the data from the previous years’ surveys or what scientists call the entire survey data set.

The net itself is approximately 40 metres long and has over 70 different parts. It has a small mesh liner in the narrow end, which makes it effective for collecting samples of both young and adults of many different species.

“We use different gear than the fish harvesters. They’re in it to maximize their harvest. They’ll use fish finders, word-of-mouth and other tools to find where the fish are and catch them,” Sheppard explained. “That’s not what we do. We will fish across a very broad area using tools like the modified shrimp trawl net, and in the same way every year. By keeping methods unchanged, scientists are able to evaluate population health and provide advice for sustainable fisheries.”

Sheppard’s job is also to support the vessels conducting the multi-species surveys, specifically through purchasing trawl gear and ensuring it meets the needs of the scientists and high standards required for research. He also coordinates the ongoing exchange between DFO science and Coast Guard before, during and after at-sea surveys.

Sheppard started his career at DFO as a laboratory technician, before becoming responsible for overseeing the logistics of how DFO collects data at sea in the Newfoundland and Labrador region. This involves maintaining science gear and the gear specification manuals.

These manuals are very important because they help to ensure that the trawl is in the same configuration and performs the same year over year. It also ensures that data is comparable from one year to the next. Ultimately, this is vital to DFO science and its ability to conduct sound science and provide advice to fisheries managers about how fish stocks are doing.

“To provide advice weighted in scientific evidence, we need to know what’s changing in the environment,” he explained. “We are aware of and observe impacts of climate change, ocean acidification, how species interact and how these interactions change as fish populations contract and grow, and other things that are happening in the environment.”

So, unlike fish harvesters, DFO researchers are not targeting a specific species, but instead sampling the benthic ecosystem (the ecosystem near the bottom of the ocean) because it provides them with important information about how many species and the ecosystem is doing.

“Each time that the net hits the bottom of the ocean we are able to collect more clues to help inform us about what exactly is happening,” Sheppard adds.

The current number of planned shrimp trawl net tows for each survey is 478 tows in the spring and 674 for the fall.

Since DFO is only interested in sampling the local environment (and not fish moving in and out of the area) at each site, the net remains on bottom of the ocean for just 15 minutes.

The sea is a challenging environment for conducting science. Fall weather, mechanical issues and logistics can impact sea time. Despite planning for some delays, the number of tows realized can be less than that planned. Fortunately, lost tows or sea time have not impacted the quality of the data.

The manual for the survey trawl was originally created in 1993 and went through several minor reviews in 2007, 2009 and again in 2015. It’s currently going through another, more thorough, review.

The manual is a very important guide for people like Sheppard because it shows him and his team how the net should be built and how it should perform.

That’s where Dr. Truong Nguyen comes in.

On paper he’s a science aquatic biologist but he describes himself as a gear technologist.

Nguyen didn’t know much about gear technology when he first applied for his bachelor of science in fishing gear technology in Vietnam nearly 20 years ago, but during his time at university and subsequent years in public service, he developed a keen interest in it and has become an expert in the inner-workings of the shrimp trawl net.

In 2011, Nguyen moved to Canada to do a doctoral degree at the Fisheries and Marine Institute where he learned a lot about fishing.

“It turns out that catching fish requires substantial knowledge of science and engineering. It’s not just about catching more fish, but rather how we catch fish sustainably in a changing ecosystem. Personally, I find the field science very interesting.”

Dr. Truong Nguyen, science aquatic biologist

Dr. Nguyen is leading the review of the 2009 Survey Trawl Operations Manual for the shrimp trawl net, as well as streamlining quality controls and standardizing how the entire survey trawl is conducted by DFO Science.

“It’s important that I learn more about stock assessment of marine resources, while researching how the survey trawl is performing. They are intimately linked together. I am investigating how the performance of trawl survey gear can be adjusted to improve the accuracy of our fish populations estimates.”

In 2015, DFO contracted the Marine Institute to revise the survey trawl drawings (similar to engineering plans), to show some of the technical changes. The drawings and parts list are used to purchase, construct, repair and quality control check the trawl in a standard manner.

Part of Nguyen’s work will be to do a comprehensive review of the manual, which will include updating the 2015 drawings to include any new technical changes.

“The manual really is a user’s guide, procurement guide, construction and repair guide and a quality control/assurance guide for biologists, manufacturers and fishing crews. It is the foundation of our efforts to standardize how we conduct the multi-species survey.”

Their goal for version 2.0 of the manual, which is expected to be completed before the 2019 fall survey, is to make the process simpler for everyone or, as Sheppard puts it, to “improve the manual, but not change our procedure.”

Trawl performance can vary from tow to tow. Therefore, during the annual surveys researchers use different technologies to take the subjectivity out of determining the success of each tow. They use acoustic instruments to monitor trawl performance and measure and reduce variability in performance. Researchers also use real-time computer programs to determine if the tows are within specified standards (for example, if the net was on the bottom of the ocean for enough time).

The procedure manual and efforts by Nguyen will be more important than ever in the coming years.

The CCGS Alfred Needler and CCGS Teleost are due to be replaced in the next few years. When a new vessel comes, they’ll do a whole suite of comparative fishing; fishing the new vessel side by side with the old vessel in the same area at the same time. This is necessary to ensure consistency and understand how the results of new vessels will relate to those from previous years.

This will be a major undertaking and will require considerable planning by both Coast Guard and DFO.

If they change their technique, they would have to break the 30-year time series and start a new one, basically eliminating the trends.

“If you have to break that time series you can’t rely on it anymore,” Sheppard warns. “You would need to have several years of a new time series under your belt before you can start making any sort of confident predictions into what the stocks are doing.”

“Once the net has been pulled up and the catch is on the boat, it is sorted by species and we do considerable processing. Among other things, we measure length, weight, gut content, weight of all the organs, remove ear bones for aging studies and determine the sex and maturity of many fish species. We also conduct extensive measurements of shellfish species, gathering detailed size information and record the maturity stage. Further, a large number of additional samples are frozen and brought back to the DFO labs where we basically study the fish from tip to tail.”

Once this work is completed, the remainder of the carcass is discarded, whether at sea or in the lab. Other items, for example corals and sponges, may also be returned to the lab for further study.”

“Fish and shellfish stocks are a big resource for Canada and for Newfoundland and Labrador, so it’s critical for us to know what’s going on. For example, these surveys provide key information to the stock assessments of Northern shrimp, snow crab, several cod stocks, turbot, among many other resources. Data is collected and synthesized about the overall state of the marine ecosystem and also about the physical oceanographic conditions (e.g. temperature and salinity) across a wide-ranging area. This all feeds into the stock assessments we conduct, and the scientific advice that we provide to fisheries managers, Sheppard explained.”

It’s DFO’s fisheries managers who then consult with stakeholders and make the management decisions about the fish stocks — taking socio-economics and science into consideration.

“In addition, many of the stocks straddle Canada’s 200-mile Exclusive Economic Zone into international waters, so these surveys are also a critical component of the scientific advice generated in international forums. We recognize that we have a key role to play in providing advice on the status of fisheries resources and whether current harvest levels are sustainable. The livelihoods of many Canadians and Newfoundlanders and Labradorians are connected to these resources, so we do our utmost to ensure the data we collect is done to exacting standards.” Sheppard adds.

Sheppard admits he’s only one part of the puzzle, but he’s very passionate about how his work affects fish harvesters in the province.

“I provide the nets and make sure the nets meet our standards and I provide the manual. We provide the raw facts, we don’t interpret that data but it’s a critical cog in the wheel.”

Close collaboration between CCG and DFO is unquestionably the most critical element of the multi-species trawl surveys, particularly with respect to quality controls, construction and repairs of trawl and issues related to survey operations. The survey manual and its trawl survey protocols provide a mechanism for effective communication and consistency among scientific staff and CCG officers and crew of the research vessel.

This dedication to consistency and rigorous science contributes to the goal of the Department and harvesters alike — a sustainable and prosperous fishery now and for future generations of Newfoundlanders and Labradorians.